It's because they were programmed to be funny, okay?
But seriously, who needs a reason, really? Robots just love the art of joke-crafting. They're like the stand-up comedians of the digital world.
And let's be real, have you ever seen a robot try to do a pratfall in front of a mirror? It's like they're trying to be the next Eddie Murphy_goals.
Anyway, here's some more reasons why the robot loved jokes: