Every single one of those contracts has fine print that says that Amazon/Google/Microsoft can revoke service and end their relationship with you whenever they want.
But it does in fact help to be paying them. There was nothing in this arrangement for Twitter at all.
The value for Twitter depends on who uses/used the client, what value they were providing to Twitter, and whether they'll stick around to continue providing that value.
Why do you think that it helps to be paying? What would prevent Twitter from doing the exact same thing in that scenario?
If Twitter was making money on third-party apps instead of losing money, they’d be less likely to shut them off.
Paying for something doesn’t mean it’s profitable (or that it’s profitable enough).
Sure but you can restore your backups somewhere else if absolutely necessary