I made a video essay on this just because why not. Watch it here if you want.
tl;dw version: Basically they're removing it because it's outdated and wasn't a good BG to ever begin with. Demolishers are bad and weak compared to just zerging gates and fighting the enemy back to drop bombs, turrets are garbage and worthless, the battleground map is bad because gates 3 and 4 (yellow sun and relic chamber) turn into congested fuckfests of blob vs. blob with literally zero real strategy involved and to "Redesign" the map essentially means that'd have to be changed into an entirely new BG.
So there you go. Your thoughts?