Ok, let me ask this question: what about LM is not funny?
That's one of those impossible questions to answer. What isn't funny about anything? Humor is not the natural state of most things; they need reasons to be funny. And even when things are funny, trying to describe just why they're funny is a difficult matter (and tends to be like dissecting a balloon; you don't learn much, and you destroy the joy.)
I may be able to describe some things that I don't like about his work, but any of those would be largely forgiven if the strip tickled my funnybone. It doesn't.

(This is not to say anything against those who find humor in his work; he clearly entertains some people, and more power to him for bringing some joy into their life and to them for finding that joy. Because of some of his rendering strengths, I generally don't skip looking at the strip altogether if I'm reading the paper... something that's not true of such "funnies" as Sylvia and Crock.)