the constant shifting of the faction blance on shards, is mostly due to one thing:
As soon as people from one faction realise they are under represented / the other side dominates the shard they are on, they will start queuing up in group finder, looking for groups on different shards where they will have an easier time (getting their WQs done, or just farming kills for the veteran achievements (the ones where you have to farm 1000HKs in the given zone in WM)).
The above sometimes leads to another situation:
you end up on a shard where it’s virtually impossible to find a single member of the opposing faction on a shard, to get a kill required for the battle of Nazjatar 
Forcing you to queue and jump shards too…
I play on Steamwheedle Cartel - when I turn WM on, the Alliance is pretty much everywhere. It’s great for situation where we want to farm kills, and can pretty much make a group to just do that, knowing that there will be plenty of opposition to fight.
On the other hand - getting WQs done is virtually impossible (even in a 5 man group) … forcing you to jump to a different shard… It’s an endless circle
And I doubt that Blizzard can do anything about it, without some radical design changes. For now I don’t have a problem - I will just jump to a different shard when I need it, or make a raid group on my shard (adding something like “Plenty of Alliance” (or Horde) into description, results in getting the full 40man roster in no time ;> ).