Or can be that in the "West" (in this case, USA, Steam as company is originally from there, if I am not mistaken, even if they have opened subsidiaries around) we are used to assume that anime=ecchi/hentai (I am not an expert, but I remember these are specific terms), without many realising that stuff like Mazinga, Goldrake, Jeeg Robot, the Heidi cartoons, etc. (well, old stuff I know) would also AFAIK count as "anime" in Japan, but they had not sexual content.
OK, in one of the first two there was the female robot shooting boob missiles and guys that tried to see naked the pilot of the femal robot, but there are teenager movies with more sexual content than that.
Point being, since they do not really have (or want to spend the money to get) the resources needed to sistematically check all the games and updates, the moment they see "anime", they go "deep diving bombing mode", hence they spot and block the game immediately, while for others that do not have that label, they may even violate explicitly their guidelines or be worst, but will not be blocked.
It's the same with Patreon, there are games and video content creators with forced sex and/or bestiality and/or incest on Patreon, but a developer I know of got threated of being kicked out unless he eliminated incest and bestiality and even if he made available a patch to reactivate it outside Patreon.