it's one of two things, or maybe both.
It could be that the show itself garners a lot of fan art because of people's politics on the internet today. It's a show with a strong female character, which automatically means there's a large pick of people who like it by default, and people who need to signal it to others.
Or it could be that in today's internet culture, you get a lot of artists trying to get their name out, and the easiest way to get discovered is to create fan art, because people are going to be searching for those tags more often than they are going to try and find your OC. As such, it pays to jump on the bandwagon early, and to just create fan art of something just as soon as there's something to make fan art of.