I noticed with my own family that the worst jokes become almost ritualistic - my uncle will deliver the same pun about wood every barbecue, and at this point we laugh before he even finishes because the whole thing is familiar comfort wrapped in groan-inducing delivery. I think you're not just conditioned, but also riding on the predictability itself; there's a weird pleasure in knowing exactly where a joke is going and watching someone commit fully to something so intentionally bad. The repetition over years actually strengthens it, because the joke stops being about the punchline and becomes about the relationship and the shared history of "oh god, here we go again.