First of all, most people who use anime avatars and female avatars are anime lovers. They may use these avatars because they are fans of this cartoon or this character, and they will use this cartoon avatar to express their preferences. And many characters in anime are official cp. If you use anime as your avatar, you can also make a couple's avatar, so you can use it with your boyfriend.
Secondly, some people who use anime avatars don't watch anime at all, just because the characters in anime are more beautiful and the colors are more beautiful, so they use avatars.
There are still some people who don't care what the avatar is and don't change it for several years. They saw others using anime avatars, so they used them themselves.