Of all the things that could have persisted from that era, why clowns? Why not heralds, or thatchers... or even gigantic flagons of ale?
Well, in the case of heralds and thatchers, it's simple. They're not needed. Nobody has a thatched roof these days, and people rarely require someone prancing about in front of them announcing their arrival. As for gigantic flagons of ale, who knows, maybe the 64oz Super Big Gulp is a descendent.
But why clowns? Do we still need them? Is there anyone out there that honestly thinks they're entertaining or funny? I don't think so. In fact, a disturbingly large number of people are actually afraid of clowns! And I'm not just talking about reclusive weirdos who think their fingers are cheese. These are normal, well-adjusted, hard-working, average-looking people that jump out of their skins at the mere mention of a clown. And for some reason, society is okay with that.
There's a reason you'll never hear about a person with a phobia of sitcoms. Sitcoms are there for entertainment, and entertainment should not freak people out. At its worst a sitcom may be cliché, or maybe even mildly offensive, but you'll never see a sitcom starring as the antagonist in a horror flick.
To draw a parallel, clowns are to the middle ages what alligators are to the Jurassic period. They give us a glimpse into a world long dead and, from a purely academic perspective, are an interesting object of study. But they shouldn't be allowed to roam freely among us, and you certainly wouldn't want your children anywhere near one.