Like others said, they're fun and magical. They're also the most relatable of the supernaturals because they look like regular humans and a human could easily insert themselves into the role of one, and in real life they are historically the most "realistic" and people who practice witchcraft still exist throughout many cultures. There is also a feminist and progressive aspect, where witches symbolize women and minorities who have been opressed and discriminated against for the powers within them but learn to harness and be proud of what makes them different. As a little girl I was obsessed with Hermoine from Harry Potter and Sabrina the teenage witch. They represented the kind of intelligent and strong while still being good and kind young women that I admired, with a lot of magic involved.
