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?
This is largely cultural, though. Some places prefer soups over western street food, but just because the culture prefers soup overall, and eat them for almost all meals. This is not the case for the global North, in my experience.