>>21394355The whole thing about mustard probably comes from Chicago. There was a lot of controversy surrounding poor quality meat and meat spoilage back at the turn of the century, and the Jungle had just been published. Chicago meatpackers in particular had a bad reputation, so they started trying to advertise based on the purity and cleanliness of their products.
Ketchup back then was very different than now, Heinz pioneered what is now the standard tomato ketchup. Other ketchups were made out of weird mixtures and blends, and had really strong flavors used to hide spoiling, rotten meat odors. It was a commonly used product because refrigeration and quality were basically nonexistent until it became widespread and the USDA/FDA really stepped up their game as far as making sure you weren't eating fucking rat meat.
Because of this and all the purity advertising around meat, Chicago folks really rejected ketchup as a condiment. Mustard and all the other garden variety toppings became the standard there because they supposedly allowed a customer to tell if what they were eating was actually good. That weird fucking baggage stuck around and now you have swathes of people who hate ketchup on hot dogs.
tl;dr
>old recipes for ketchup hid spoiled meat, tasted like ass. Mustard didn't