wanting to own all ads placed against user content

wanting to lock users in and make it harder to leave for another service and still maintain a presence (which is also a constant ad for that other service) by cross-posting

wanting to make it harder to see the stuff you're following people for without ads inserted every few posts

It s still possible to leave but nobody leaves. Surely they benefit from some extra safeguards, but i don't think either are worried that users will take their data elsewhere. Usually when a new platform emerges, it 's a new format (e.g. tiktok).

I 'm pretty sure their response was in order to avoid bad PR during the Analytica scandal period.

As I understand it for Twitter in particular, third-party apps were limiting the reach of their business-related tactics that users hated. Namely, none of those apps implemented any kind of invasive advertising, tracking, and recommendations – which made those apps much better from the UX standpoint than the official ones.

A mixture of bad tech legislation, concerns over Russian interference, and good old-fashioned anti-competitive tendencies.

Having itself supplanted MySpace, Facebook is in a good position to see how easy data-exports can help competitors supplant a dominant company.

3rd-party clients are also a good way to remove ads and tracking, which is obviously not in Twitter or Facebook's best financial interest.

Yet they still provide with tools to export all data . So i don't think the migration of users is a major concern for them.

I 'm personally all in favor of making the APIs open and unlimited again, but within a month you 'll have journalists nagging again

Export tools happened after GDPR.

they existed long before gdpr, e.g.:

https://www.askdavetaylor.com/export-data-facebook/

This fight is much older than that. If you want to get sad, read this: https://en.wikipedia.org/wiki/FriendFeed