What’s the origin of ‘Why did the chicken cross the road’ jokes? I mean, really, how does a joke like that become so popular?
I don’t think you’ll ever find the origin of the joke: it goes back to 19th-century vaudeville and no doubt was stolen from yet earlier versions (back to the Greek comedies, I wouldn’t be surprised).
As to why it’s so popular: it’s a classic, simple, non-dirty and easily understood joke, with lots of possible sub-jokes springing out of it.