Because he fucked up. He either gave some same-level permissions to some retards he couldn't trust, or he created some kind of an outlined community/business setup that actually allows him to be ousted.

At its core, all open source is, is making a project or product's source code available for public use and redistribution. There are of course different open source licenses with different kinds of rules and conditions. And like I already said in another comment, what license is used is totally up to the project lead.