Once Microsoft owns them Activision no longer has a say, and they have a vested interest to discourage players from waiting for the games to come to the service over buying them now.

I was curious so I looked up how long it took after the Bethesda acquisition for Bethesda games to hit Gamepass; it was three days. I could be wrong, but I don’t see Microsoft letting a holiday season go by without the war chest of games they just paid billions for on their flagship service.

Anyone that was going to buy D4 already bought it. I can't imagine they're getting (m)any new players with all of the negative spin on the game since it came out.

Releasing it on gamepass when the first paid expansion is coming out would be the best way to monetize it.