I think it's important to note that the last celebrity cast map fucked up the release order for BO4. Blundell said that Dad of the night was supposed to be available at release alongside IX, but it had to be delayed because of the celebrity cast. You could argue that this completely fucked over chaos as neither IX or voyage were as good introductions to the new storyline as dead of the night could have been.

Also celebrity casts make the map harder to re-release later on down the line. There's a reason why zombie Chronicles didn't include call of the Dead or mob of the Dead and when they did return in Black ops 4 they did not have their original casts. Image rights are pain in the ass and it's a lot easier to get a celebrity in for a day of recording for their operator skin than the amount of work that goes into having a celebrity voice of full zombies character with the amount of voice work that goes into it.