Why do people put ketchup on their hotdogs?!

Why do people put ketchup on their hotdogs?

Im from Chicago and if you would even think about asking someone to put ketchup on they would give you a dirty look. Some places would even kick you out. But I was in St. Louis and got a hotdog and their was ketchup on it. I was like WTF? It didnt taste nearly as good either as a chicago dog.

17 hours ago
I meant *there

I don't know, but my 9 year old does it. and it's disturbing. I remember that Dirty Harry movie, when he asks the same thing.
(what movie was that? Dead Pool?)