From my taste (as a foreigner) ketchup is disgusting on its own, I prefer it to be mixed with chili sauce
Most of the people who exclusively use ketchup as condiment are children who can't hold their chili sauce yet (and some adult who can't eat spicy)
But yeah, as it's more available and cheaper condiment than mustard, we frequently use it on "Western food" (hot dog, burger, grilled sausage, etc.) along with mayo and chili sauce.
I think your people obsession to ketchup is comparable to our obsession of chili sauce. I even heard my friend eating in expensive sushi restaurant, then whipped out sachets of chili sauce to eat the sushi with. Blasphemous.