If I remember correctly, there was a lot of discussion about what should constitute a genre tag and what shouldn’t, and people tended to have strong feelings about it. In the end I believe it was decided to keep genres “clean and tidy” and allow users to only add content tags. I tried to find a reference to that (I remember it so clearly), but this is the best match I could find:
I’m sure there’s something more official somewhere?
Of course if users aren’t allowed to create genre tags, the UI shouldn’t be misleading about it, I agree. 
