> 100x less memory and was much more performant
Technically you're not prevented from doing so - you would just have to keep it to yourself (/family/friends/etc). Non-technical people rarely care about these things.
> backstabbing developers
I don't disagree. Would be interesting if there are any stats on who/what made Twitter popular, got any?
> And why is that a problem?
It's a problem for Twitter when you're trying to run a top-brand. Clients who don't keep up-to-date actually make Twitter look bad to the public. It also makes it harder for Twitter to innovate, move quickly (and probably get usage stats), without coordinating with external developers.
Apple actually does (in some aspects) force developers to keep their apps up to date. I develop iOS apps and this actually consumes way more time than I wish it did.
Your concerns are valid from a third-party concern but from Twitter's first-party concern they are distractions.