When I was a kid (decades ago) I used to put both mustard and ketchup together on many things.... haven’t even been tempted to do that in a great many years.
Put it on French fries and you don't really taste the potato.
So I can't even contemplate using ketchup nowadays.
But if I go to a fast food joint and they put it on the burgers, I don't really mind it - even kind of like it.