They aren’t, they’re supposed to replace flanking. Like I said earlier, I find flanking makes it too easy to gain advantage in 5e. Facing allows you to gain advantage from tactical positioning, but makes doing so more difficult to achieve. I find, in this edition, it gives me more of what I want out of a flanking rule than flanking does.
Right, that’s the point. Facing emulates flanking, but does it in a way where the necessary positioning is more precise than the flanking rule does, making it more worth granting advantage for.