If you don’t like your low or mid pop server, then transfer to, or reroll on a high pop one. Some of us actually like not having to fight with 50 other people for every herb, mob and ground spawn in the game.
Also, server populations are always low at the end of an xpac. Doubly so, when it’s the end of a bad xpac. Server pops will jump again when Shadowlands is released, so Blizzard has to be prepared for that. That means not merging servers if they’d be too big once the release drops.