Neat comment from @Gargron just now:
"Mastodon was built on the API-first principle."
This is important because a whole lot of 3rd party app developers were promised "openness" by Twitter -- and those promises were broken.
3rd party development is where so much innovation happens!
@atomicpoet @Gargron
Well, note also the issue of "perverse incentives".
Companies like Twitter, Facebook, Instagram, YouTube, Vimeo etc are all threatened by the possibility of a 3rd party app interfering with their revenue flows. Having an API creates the illusion of openness, but constantly changing it makes competition ineffective.
This is a non-issue for open-source distributed media like Mastodon (or any Fediverse software). It's a free market, not a closed shop.