One probably has to be of a certain age, but the punchline is, “Because the bicyclists done took everything else.”
They make it look painful… or maybe they’re just guarding against a free kick.
My guess is that these are competitors in the 10k, 24" category. Try riding a 24" unicycle with 125mm cranks 10k as fast as you can. That’s what you’ll look like. Or like this (yup, the girls are doing it too):
