That's not Facebook moving to an alternative store, that's Facebook the company introducing another application outside of the store.
Also worth noting that they got called out and ultimately shut down for being shady. Even though they were operating outside of Apples locked down environment. It's almost like we don't need Apple to protect us, and in fact we can protect ourselves
B) if people truly value the Apple lock down system, they will not use applications that don't comply with the lock down system