What’s wrong with ketchup on hot dogs?
Nothing. People just like to judge other people's (or Midwestern city's) food choices.
It's a metaphor for gaming preferences and intolerances, and it's been fascinating watching it take different shapes over the last few months.
From what I can tell, it started out as pizza and its various toppings being a metaphor for the D&D game and all of the different elements that people enjoy in it. This happened around the time that there were tons of threads on the forums about optional rules, changes to game lore, and new character options in
Tasha's Cauldron of Everything. I think I started that one, or at least heavily influenced it, as a way to encourage discourse without upsetting too many people...a gentle way of reminding folks that preferences aren't facts, and nobody is going to force you to 'eat something you don't like.' (It's also a way to poke fun at people who absolutely cannot abide anyone disagreeing with them.)
The discussion then migrated to sandwiches when it was suggested that pizza is a type of sandwich...which I thought was a fascinating way of discussing that D&D is an RPG, but not all RPGs are D&D. This metaphor usually comes along when some major campaign setting starts getting traction in the forums...
Dark Sun was grinding around in the rumor mill for the first shift in this direction, then it was
Witchlight, now it's
Spelljammer.
In the latest twist on this metaphor, the topic has shifted to hot dogs, because they are sandwiches in every way that matters except for their name--which coincided with several recent threads on "retroclones" and the next edition of D&D.
If there are any sociology or psychology grad students in the forum, I bet there's a thesis in here somewhere.