Tags like "anal" obviously serve a completely different purpose. People who don't like that fetish can exclude it in the exclude tab. People who have several fetishes can filter for games who contain them all, anal included. So if you like games with virgins, milfs, anal, foot fetish and BDSM and you filter for those tags, you gon' find games who have it all.
If you however search for animated games and then you'll get displayed games with 10 hours of content, 100 sex scenes but only 5 animations which take up 3 minutes of these 10 hours, you obviously did not found what you were looking for.
A game like Summertime Saga can add that tag with good faith because everyone who likes animations will have them in every scene. A game that has more animations than no animations can also add it, since it will most likely make most fans of animated games happy too. Some still pictures inbetween are common. But a game that barely has animations isn't really what people are looking for if they filter for that tag.