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
I 'm pretty sure their response was in order to avoid bad PR during the Analytica scandal period.
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.
I 'm personally all in favor of making the APIs open and unlimited again, but within a month you 'll have journalists nagging again