I'm shocked it's only 25. I would have expected an order of magnitude more given the number of features and sheer reach of Twitter. That can't possibly be right

I'm shocked it's only 25. I would have expected an order of magnitude more given the number of features and sheer reach of Twitter. That can't possibly be right. Not sarcasm btw. I think you're underestimating how much work there is. First, there are a ton of features: lazy-loading tweets, retweet, favorite, lists, all the stuff related to analytics, settings. Simply maintaining that stuff with security updates and bugfixes is a significant commitment. Then there's accessibility and localization to consider. Next there's fix and feature experimentation. They probably don't release new features and fixes to everyone at once. Instead they roll them out slowly, or show different versions to different users, compare, analyze and iterate. Browsers update approximately every 6 weeks, so that's something to keep abreast of. At Twitter's scale, a CSS rendering bug that affects 0.1% of sessions will be seen by hundreds of thousands of users. And it's not just "a Twitter client". It's THE Twitter client - the canonical one. It has to have higher standards of performance, quality, and reliability than a random Twitter Android or iPhone app.