Maybe I'm mistaken, but it had been widely reported that Twitter was near bankruptcy. It was also widely reported that Musk was seeking ad revenue as well as shuffling this gs around within the company in an attempt to turn things around.
If so, I see this as one of the things Musk deems necessary to accomplish his goal. Unfortunately, it'll cause a few favorite Twitter clients to no longer be available to access the service. Still, favorite products and services fall by the wayside all the time. Dark Sky and Vine to name a few.
Even if true, this will no draw many people back into Twitter's main app, so they will not make money from those users; they will lose that revenue stream, because they won't be able to sell them as "active users of the platform".
The issue is that Twitter lied to developers and users around this. They cut access on 2023-01-12, then posted Tuesday that they were enforcing a long standing policy, for finally issuing the said policy yesterday.
It's one thing to say "yeah, we don't want third-party clients going forward and you have 1-3 months to leave", and a completely another to say "yeah, you're gone because you're didn't respect our policy, that we have not yet published and that we won't publish for another week".
I really hope Twitter declares bankruptcy and brings down Musk along for the ride. And that both reimburse the third-party developers for the fees that they will incur because of their reckless actions.