I think Blizzard feels at a loss to add BGs unless there’s some sort of lore reason for it. The Alliance and Horde need to be fighting over something in order for a BG to be made. The last BG they gave us was Seething Shore, which was in BFA. Prior to that, the last one was Ashran, and they made up a contrived reason for that, like some BS about the Alliance and Horde having a massive war over some ogre relics that never mattered to the story and were never mentioned again.
Blizz doesn’t seem to understand that PvPers do not care what the context is. There doesn’t need to be a context. Does it matter what the context is when you’re fighting over flags? When you’re playing keep away with orbs in Kotmogu?
If they made a BG in Zereth Mortis with the same concept as collecting orbs as Kotmogu, and it was fun, people would play it. There doesn’t need to be any reason given, or it could be some really simple reason like 3rd party actors like Ethereals or a Broker hiring people on for tests or to do their dirty work for them, or whatever. It doesn’t need to be an Alliance and Horde war.
They just need to give us more maps with more variety, even if they’re the same game modes that already exist.