Because they're creepy as fuck and when I was 7 I saw a horror show about clowns that I wasn't supposed to see (it was on a horror channel and I accidentally started watching it and couldn't stop) and it basically traumatized me.
Mine was about this boy who's deathly afraid of clowns and then they start stalking him and they're fucking everywhere and then he's peer pressured into going to the circus and he gets captured by them and asdfghjkl