FWIW, they added the ability for these companies to control their own integrations by publishing iOS and Mac apps. It's just that so far, only Twitter has both

FWIW, they added the ability for these companies to control their own integrations by publishing iOS and Mac apps. It's just that so far, only Twitter has bothered to do so on Mac. Even software like Slack which does so for iOS just hasn't bothered to port that code to their Mac app - most likely because of the Mac app using a different Electron-based codebase.