It's always been said that the hardest form or genre of writing to create is comedy. Suspense, thrillers, horror, sci-fi, fantasy, romance, and all manner of fictional novels are a walk in the park compared to trying to write something that will make people laugh from beginning to end. What increases the difficulty is that you also have to create an interesting story to go along with the comedy, or else things get very boring very fast.
The writer's who are able to accomplish this best are usually the satirists because they have a point in mind beyond making you laugh. If the writer's sole intent is to be funny or even if being funny shares equal billing with plot, characterization, and all those other things that serious novelists consider important, the result is that the things that make a novel a novel suffers accordingly.
So it's very serious business when an author sets out to write a funny novel. He or she has to decide how they are going to make it funny. Are the characters going to be funny people doing funny things in a funny world? Or is the novelist going to "play it straight" (which has nothing to do with sexual orientation, and doesn't preclude having gay characters) where things are funny because of what happens to those involved and not because of whom they are?
This is one of the things that I would think that makes comedy so hard to write, all the pre-planning that must be involved. Everything you write has to contribute to the "funniness" of the final result as well as make the story click along. The last thing you want is someone laughing at your story because it's fallen ass over teakettle off of its plot line with all the aplomb of someone falling off their six inch stiletto heels. (Hence the story line clicking along bit – think about it.)
Don't think for a moment that those asshole reviewers aren't all waiting out there for you to do just that – they'll sharpen their pens and fill them with that special spite ink they save for just such an occasion and slap you about with so much backhanded praise you'll be bruised for joy and wish they'd have had the honesty to say they thought it sucked as a novel, not said stuff like quite a lot of really funny bits tied together with a flimsy excuse of a plot so that even more funny bits could be written.