I gave a fairly short answer, talking about how the series brought in various elements of satire, parody, irony and absurdity which all appealed to humour touch points for me. In the end, though, I concluded that one either gets humour, or one does not and there is little that others can say that would explain a joke funny to somebody who does not share the same sense of humour.
So I concluded, "Some of us find it funny because it is funny."
When I probe into the essence of what makes me laugh though, it occurs to me that my sense of humour has changed considerably over the years. While my late-teens self might disagree if we were to meet today, I think that my sense of humour is more sophisticated now than it was at one time. I have seen enough episodes of Regular Show and Adventure Time to know that the shows do not hold a strong appeal for me. I don't hate them, but the flavour of shallow absurdism that seems to drive the humour and the plot lines gets very thin very quickly. Yet I can see how I might have liked these shows 30-35 years ago.
On the other hand, I have really enjoyed shows like Simpsons, South Park and even Beavis & Butthead (seriously, the movie was great) where there is no less absurdity, but it is layered like a syrup over a dense foundation of satire. The first time I saw This Is Spinal Tap I nearly laughed myself to incontinence. I guess I could say that I prefer my humour to make a statement on the human condition.
Does this mean that I don't like absurdity unless it is steeped in satire or irony? If so, then how does that explain my love for Monty Python's Flying Circus? I don't think I could find a trout large enough to beat any social commentary out of their sketch on the Ministry of Silly Walks, for instance.
Again, I find that I simply have to fall back on the explanation that it is funny because it is funny. Somewhere in my brain, certain visuals, concepts, or sounds can trigger pathways that my mind finds pleasing in an amusing way. I cannot explain how it is wired, or why some things simply strike me as funny. If I could remove my brain and plug it into a machine to track my mental pathways, I would be dead. But somebody else might be able to trace the pathways and explain it to you. Let's not do that and leave it as a thought experiment for now.