I'm not certain of their motivations behind creating this wbplay website/account registration.
But informally, I looks like WB is trying to create their own version of Steam and Origin, a specific games store/client just for their specific games.
Or maybe a social network for their games.
It's an endeavor that can be a bit tricky.
One of my major mmos keeps insisting I use their client program instead of the standalone launcher to play the game.
I've refused to do so because it's not designed to support the game I am playing in any way.
It's just an advertising tool for all their other games, which I have no interest in, so don't want to install it just to be annoyed with "incentives" to play games I find dull.
I hope wbplay isn't an attempt to do the same thing, get people who play one game to play them all and keep reminding them if they don't.