Even on ACR I see only 1 table of 9-max or two, amost always occupied with a long wait list.
I noticed this also, when I last visited the ACR lobby. Full ring cash tables still exist, but they dont draw a lot of activity.
The rooms want more variance, craziness and volatility, maybe also more rake through 6-max. (more frequently in the blinds).
It is mainly a question of player preferences. PokerStars did not remove their Zoom full ring tables (other than 2NL) to earn more rake. They removed them, because they stopped playing and never started again. Its easier to get a regular table started, because it only requires two players. But even so if few people wants to play a certain game, it makes little sense for a
poker site to continue offering it. Better then to focus on those games, that are more popular.