I get why things like hot dogs or bratwurst are readily available as streetfood, it's logistically easy - but so is soup! You need like a pot, maybe two if you're getting crazy with it, maybe some bread rolls and that's it. It's cheap to make, cheap to buy, you could get hot soup on a cold day to warm you up or something like a gazpach or okroshka on a cold day to have a chilling meal. They're stupidly easy to make, all the ingredients basically cost zilch, very easy to adjust for all kinds of different dietary needs if you offer some sort of toppings optionally instead of throwing it all in there.
So why isn't there more soup? It's a style of meal you can find in basically any cuisine yet in all my travels I remember like two instances where I could just get a soup. What drives streetfood and why is soup shafted?
I dunno, depends on the location? For some it's definitely part of life like ones that post up near workers where your only alternative is driving. The streetfood in some cases becomes your regular lunch.
Like maybe that's quite a "treat" lunch but the convenience of closer means they get to go sit around more rather than spend their break travelling to and from their alternative lunch options. Sure bringing lunch from home is the cheapest but I know I've been in that situation before and not everyone is making particularly sensible spending habit choices at all times.
I'm thinking more like urban center, pedestrianized spaces here honestly, not so much Ex-Urb with a foodtruck if that helps contextualize it.