Earlier this month, pretty much all of the third-party Twitter clients stopped working which has since been confirmed by the platform, that this was an intentional move. The reasoning behind it was supposedly due to some rules being broken, of which were unconfirmed. However, since then Engadget spotted an updated developer agreement that is now saying that developers are not able to “create a substitute or similar service or product to the Twitter Applications.”
Twitter has intentionally banned all third-party apps overnight and then quietly updated the rules to ban those apps, such as Tweetbot, Twitterrific, Aviary, Echofon and Birdie. The wording makes it pretty clear that these apps will not be coming back. The official advice from Twitter is that users who are affected by this should just now use the official Twitter app.
The main reason that we can come up with for Twitter banning all third-party apps, is money. When all users are using the official Twitter app, the company can funnel people into Twitter Blue and then serve more ads.