Lemmy providing an open API does not mean that third parties maintain compatibility forever. (Edit: for example, what happens if the third party app gets taken away by a malicious maintainer? Or becomes buggy, or un-maintainable, project dies, etc.)

I don't want to upset you, but I think I have to say this for the sake of the community. The attitude like "we provide an API, so third parties will follow," is what is causing instance admins' distrust in the first place.