I do not know the whole process of making new tags, but one important example is in the following post:
https://e621.net/posts/3767506
This shows intercourse between two males, with a female in the background. However, this was found under a search of only the "female" tag.

This, I believe, is the reason for its downvotes, and it may do better if it wasn't able to be found by people searching for only Female art/animations

female -male_focus would usually be how you filter out images like this, though the post was actually missing the male_focus tag at the time you posted this.

I think the downvotes are probably more due to the quality of the submission. It kind of hits the uncanny valley.