It's not a very good film, but it's a role that Jim Carrey was born to play. Without him, it'd be shit on a shit sandwich, but he makes the film tolerable enough for at least one viewing every Christmas season for me.
For some reason there are a lot of people out there who happen to like this film.
I don't know why, and over recent years have stopped trying to question it.
My only hypothesis is that maybe people like it for its camp value like the way people hold fondness for The Star Wars Holiday Special or Santa Claus Conquers the Martians.
Its really the only reason that makes any sense.
I think another reason for it is that there are a lot of people who were younger when they first saw it, and there is probably a bit of a nostalgia factor for them. Had I seen it when it first came out, I probably would've liked it, but I didn't, so I don't really hold it in high regard (then again, I've never seen it). At the same time though, I still have a bit of a fondness for Pokemon: The First Movie, even though I know that it's not a good movie. So that's where my thinking comes from.