“Scary” clowns rely on a concept that is now positively quaint.
“Corruption of Innocence/Sweetness”, which used to be a pretty powerful horror/drama trope.
But much like cosmic horror, it relies on offending sensibilities that most people no longer really have. It’s not “shocking” to see something innocent corrupted of you’ve spent a few minutes in the internet with safe search off.
Just like how cosmic horror doesn’t scare us because the idea that we are a worthless speck of debris on a wet ball floating in space against a hostile background that will kill us stone dead without a seconds thought is no longer that surprising.