As for the UX thing — Twitter owes a huge amount of its own UX to third-party clients. Hell, Twitter’s own iOS client was originally a third-party client they acquired called Tweetie. The developer of Twitteriffic made a list of all the things they pioneered for Twitter: https://furbo.org/2011/03/11/twitterrific-firsts/
There are plenty of good reasons why Twitter might not be comfortable giving ads as an API, and that means they're giving away their resources for free by providing these APIs.
Also, Twitter is a more mature platform now. They probably don't feel like they need the innovation from these apps anymore. But that misses the point, small changes like the view count on tweets are added to improve engagement / profit, so Twitter wants full control of what is seen.
Again, it probably does not help Twitter to support these people, even if they are a small part of the user base. Same mindset as banning competitor links in your bio.
This isn't so much of a problem on Twitter as much as Reddit, though. Their native experience is okay (it's just the users that are insufferable)
Also you should rethink your life if you consider yourself a Twitter/Reddit power user.
I'm not, but people can make money on those platforms nowadays, so don't be so judgmental.