Couldn't they launch a paid ad-free tier that grants API access? i.e. the user pays for the ad-free experience, and the 3rd-party apps would only work for those users who have paid. I can't think of any companies who have done that but it seems like a reasonable solution.
It'd be so much better if we just paid a small sum to own our accounts on those platforms. How much would it cost? Like a Netflix subscription? That'd be worth it.
I guess one reason why that isn't possible is that the platforms only work if everyone* is there, irregardless of income. If there's a subscription fee not everyone will afford it, especially young people who are (arguably) culturally more influential.