Do you talk about the actual front page or the front page of browse? Because the actual front page is not very dominated by horror. It is featured games, bundles, jams etc.
But Horror is the most popular tag on itch. Followed by visual novel. Then simulation, then roguelike. It says so on the front page upper left corner.
In contrast to Steam the presentation is somewhat inverted. Once logged in, you are presented with a ton of recommendations and some popular games list is a minor part of the page. On itch front page, recommendations are one side scroll hidden in the middle.
So anyways, itch should not recommend horror games to you, after you liked and played some other games. But you need to go to the actual recommendation area and not the front page or browse.
(Please do not try to downvote random horror games to adjust your recommendations. Not only would this be unfair, we also do not know how much this would be weighted in contrast to your positive interactions. Furthermore, to downvote such games, you would have to interact with those games, so itch might actually be convinced you do like them horror games ;-)