The difference is that my business that depends on AWS pays for the service, and big businesses that depend on AWS have contracts about support and payment.
If this incident truly represents Twitter's change in approach to third-party clients, that change in policy is being executed in the most petty and malicious way it could be done.
This is not to excuse Twitter's actual behavior, which is clearly shitty. But: More petty and malicious would be to shut off access, then contact devs and promise that access would be restored if they just make these tiny changes to their app, and also sign this NDA forbidding discussion of the process. Then string along for a week or a month demanding just one more tiny change after change.
Then ghost.
(This is not a value judgement of Mastodon vs Twitter)