This was implemented to counter dodging, but it has some additional benefit in that people aren’t constantly joining and leaving in progress BGs in mass. Non ranking players that enjoy pvp in vanilla tend to prefer WSG and since they are often the ones keeping the queue alive, WSG is what you’re gonna get. (I’m in this crowd myself, so I like having WSG as the default BG.)
Also given the pvp population now, I doubt there are enough rankers of the right classes on either faction to keep an AB premade running constantly, so they will stick to queuing WSG as it’s easier to fill a 10man group than a 15man one and the comp/gear requirements for WSG are more flexible.
If you wish to play AB, your best bet is to form a group of 10-15 on Alliance outside of a BG weekend and queue AB without queuing WSG and inform Horde via discord or world chat - I’m sure some would rather play AB than sit in queue.