You can't compete with mindshare on that scale. The network effects are ludicrous. People have made generally better products than Facebook for years that all wither because they don't have a billion people and everyone you already know on them.

If Facebook were using an open protocol like Ostatus anyone could make a peer network that is better than Facebook and actually compete, but their userbase is entirely locked into their platform. On purpose, of course, thats why investors value FB so highly. Its entirely against their interests to enable competition.