We're talking about a profession that has been around for centuries - selling food on the street. It's the American dream, in fact, which is what is so amazing about it being a six-figure job. It's important to consider the fact that if you're the hired hand of a cart/truck, you will most likely not make this kind of money. You'll need to be the proprietor, but that only makes sense. Risk increases reward.
There is the problem of permits. You need to have proper permits depending on where you sell, and you may have to pay higher taxes as a business. All that's generally true of most businesses, so I wouldn't worry about it too much. If you handle your business right, you will be able to pay any fees or taxes and still make plenty of money.