Because there are a lot of picky and entitled asshole horror fans out there, that's why.
You've seen Guy Standeven in something because the man was in everything.

Hate is a strong word. Disliked is better. What was this movie PG-8? or whatever. The setting was good, the acting was fine, the costumes/cgi was good enough. It just leaned way too much on the comedy which made you wonder why they even bothered with the "horror". I've seen children cartoons more violent than this movie. It just felt like a joke but it wasn't funny. It tried very hard to be funny however. It made it all come off very cheap.
I personally would not have minded a much darker version with decapitations, mutilations and what not. It was my fault really because that's what I expected. You know there are movies that actually mix comedy and horror perfectly. This basically had no horror at all.
The movie to me was just boring nothing memorable happened. That's not saying the movie was bad, it was just meh. I really liked the costumes. Krampus himself was probably the most spoopy looking thing in the movie and carried it. The slow start and the weak, terrible ending really brought the movie down for me.
This movie would have been better off with only the comedy tag and not the "horror". I watched through the entire thing. At the one hour mark it kinda came to me that nothing would actually happen in this movie.