You realize the implementation of battlegroups was a result of the need for cross server pvp due to faction imbalances on individual servers right?
Back in the day BGs were queued only vs your server. A faction dominated the server and eventually drove off the opposing faction. Thus cross server play and battle groups were formed - where ally dominated servers were matched with horde dominated servers.
Are there more horde than ally? According to ironforge. io which takes into account server pop based on raid logs, across Americas servers- the faction split is 46% ally (14,179) vs 54% horde (16,437). Not a massive imbalance…
People don’t wanna queue BGs and rot away 70 hours to buy 1 piece.