It HAS them, just not built-in tooling to make using them easy. 2ndQuadrant's repmgr gets you partway there, I'm really hoping to see them revamp it now that pg_rewind is a thing to make restoring a failed master less of a pain in the butt (this is literally the only reason I don't bother with HA right now, it's usually much easier for me to get the DB back online or restore from a barman backup than deal with replication).