They say you can't go home again. (They being my parents.) In 2012 I famously quit Twitter, because they dropped support for RSS. Recently, though, I experimented with rejoining Twitter. They haven't restored RSS, but I did become somewhat nostalgic in the meantime. As with most nostalgia, it resulted in disappointment. After a few months, I've ended my experiment, and I declare it an utter failure. Twitter continues to be the worst. Even worse than before.
I believe that Twitter has (at least) two fundamental problems, one newer and one older. The "new" problem is that the new user experience is atrocious. This is what I've discovered by joining for a second time. (I had to create a new account, because I deleted my old account, and indeed someone else has appropriated my old Twitter handle.) There is very little incentive for a new Twitter user nowadays to stay with Twitter. I suspect that the majority of people, after experimenting with Twitter for a bit, will simply give up, like I did, and this suspicion seems to be confirmed by Twitter's slowing user growth rate.
When I rejoined Twitter, I already knew who to follow, because I had people I followed during my previous stint. For completely new users, however, the first hurdle is figuring out who to follow. Twitter unhelpfully suggests celebrities. These suggestions are self-defeating, because celebrities are almost guaranteed to ignore you. They have way more followers than they can respond to personally. So you can follow celebrity accounts, tweet to the celebrity accounts, and ... nothing. That gets old quickly. You can try to "personalize" your experience by telling Twitter your interests, but the categories are so broad (e.g., Music) that you end up with more celebrity accounts anyway. And you can upload your contacts to Twitter in order to discover your contacts on Twitter, but what if you don't want to provide your address book to Twitter? And while uploading your contacts may be a good way of finding people you already know on Twitter, it's not necessarily a good way of finding people you don't know. What if you're interested in, say, Mac programming, and you're new and unknown in the field, so you don't have any existing contacts? Indeed, what if you're signing up for Twitter in order to meet other people in your field? Good luck with that.
If you've already been on Twitter for a long time, you may have no idea how it feels to new users. You're probably not even interested in new users anymore, and therein lies the problem. I originally joined Twitter back in 2008 (for the defunct C4 conference). Twitter wasn't brand new at that point, but it hadn't yet hit "The Big Time". It was not overrun by the horde of celebrities and non-technical users. There was still some excitement when a new person joined Twitter, and when a new person followed you. At this point, however, any long-time Twitter user has amassed thousands of followers. Most new followers now are spammers. Understandably, you tend to turn off new follower notifications after you reach a certain level. So you may have no awareness of when someone new joins Twitter and follows you. Even if it's someone you know outside of Twitter.
How does a new user get someone's attention? Following doesn't work by itself, with no follower notifications. And because of the volume of users, and the volume of spam, you may have turned off not only new follower notifications but also mention notifications from people who you don't follow. There could be no way at all for a new user to get your attention. But you don't care, because you already have thousands of followers. Who needs one more?
Worse than indifference, there can be outright hostility to new users. Suppose you're a woman in a technical field, you sign up for Twitter, and Twitter gives you suggestions for some semi-famous podcasters to follow. You follow them, you listen to their podcasts, and you start tweeting to them. For some reason, I suppose because you're viewed by these white men as an uppity woman tweeting above your league, your tweets are viewed as suspicious, terrorist actions, and so these semi-famous, self-important, self-appointed Twitter vigilantes conspire together to cyberstalk you, discover your personal information, and out your offline identity. Welcome to Twitter! Needless to say, this is not a mere hypothetical scenario.
For the "lucky" new user who manages to acquire a small number of followers and who isn't driven away by an angry mob, Twitter is still a very lonely place. The problem of volume strikes again, i.e., their high volume and your low volume. You may have convinced some long-time Twitter users to follow you, but you're only one of thousands of their followers, and they have probably followed thousands of people themselves. So you're constantly competing for limited attention with masses of others. If you're following thousands of people, you can't possibly follow them all closely. Some Twitter users rely on lists to narrow the number of people they follow closely. But then if people are using lists and ignoring their full timeline, getting followed by someone doesn't mean much. You're nothing unless you make the "A list". Other Twitter users simply glance at their timeline whenever they feel like it, and only when they feel like it. If they happen to see one of your tweets, you may get a reply. If not, you're invisible.
If you feel invisible on Twitter, then you're not likely to stay. Long-time Twitter users don't feel invisible, because they have thousands of followers, so even if the "hit" rate is low, they're likely to get hits with their tweets. For a new user, in contrast, it usually feels like you're just tweeting into the void, and nobody likes that. It can seem as though you have no friends on Twitter. Compare this with Facebook. It goes without saying (the most ironic phrase in the English language) that Facebook is terrible. But you have a reason to stay on Facebook nonetheless. People join Facebook to keep in touch with their family. Their old school friends. Other people they know and love, or hate, in real life. As long as those people are on Facebook, you have reason to stay. Would you abandon your family? They would frown upon that, and write you out of their wills. Whereas Twitter does not have the same hold on you. Your family is not on Twitter. Hopefully. That would be embarrassing. Better protect your tweets.
So the new user experience on Twitter is awful and causes a lot of people to abandon the platform entirely. This is a fundamental problem. The other fundamental problem is that, as a social network, Twitter is not particularly social.
What does it mean to be social? Ultimately, I think it means to have a conversation. On Twitter you can follow people, but you can't follow conversations. The UI for conversations is really awkward. And the 140 character limit for tweets is not at all conducive to having an intelligent, adult conversation. Twitter encourages quips, sound bites. It's the ultimate short attention span destination, a hit and run social network.
The surest way to discourage conversations is to enable likes/favorites and retweets/reblogs. These inarticulate gestures barely qualify as social. They are literally the least amount of social interaction you can have with someone. Press a button, done. Much social, wow. They are the form letters of social networks. No personal response is required. To whom it may concern: click. I would've traded one hundred likes for one person taking the small amount of time and effort to personally reply with "I like your tweet." When my tweets got likes but no replies, it was still a very empty experience for me. It still felt like I was tweeting into the void.
Counting likes and retweets turns social interaction into a contest or a video game. Twitter is trying to trick you into thinking that if you maximize your stats, you're somehow winning. But what are you winning? What are those numbers really worth? They're worth money to advertisers, as views, but what are they worth to you, as a member of a social network? Do you feel that a superficial connection to a large number of people is more important, more rewarding than an more intimate connection to a small number of people? I don't, and that's part of why I quit Twitter. Again.