You mean those hot dog vendors have been cheating the system (and on their taxes) the whole time?
No, but when I looked at them in 2003 they were following the system rules to the letter. The rules themselves allow it.
While they're individually owned (so are most Subway, McDonald's, and Starbucks store fronts FYI), they work together with a small number of vendors for the product (food delivered pre-cooked per city specs, soda, and extras like napkins), part-time and full-time cooks, cart setup/teardown including towing and night-time storage, signage (group deal from a printer), and a few other basic services (training, cart sales, accounting/insurance group buy, etc.) were all available.
You can get a license, hire one of these companies to run it, and other than meeting the cities minimum obligations for the owner have nothing to do with it.
Few start out using these companies but they quickly find out they don't get a vacation, may run out of product on a busy day or have lots of spoil on a slow day, and experience numerous other difficulties if they don't.
You could easily run a food truck franchise in the same way. In fact, Caplansky's was quite public about their intention to franchise Toronto trucks a couple years ago on Dragon's Den. It's not a weird and wacky concept.
Franchising is about setting up an owner, who may have limited experience, with the tools and products needed to be moderately successful whele grabbing a slice of the pie. Branding/advertising is usually a large part of this but it doesn't need to be. It can be done as a straight service fee and not include a profit-share; hot-dog carts are as a service fee.
The result is that the product from one hotdog cart to the next in Toronto is very consistent with little variation. The city doesn't prevent sausage vendors from selling a wide variety of restaurant quality flavoured sausages (jalapeno, honey mustard, hearty beef and potato, etc.) so long as they're pre-cooked and served on a bun. How much variation in hotdog cart menu do you see?
A-la-carte had a ton of problems, but one of the most difficult wasn't the price. It's that the owners were unable to fall back on these service companies to ensure the cart made revenue when the owner was unable to cook, that they never ran out of product (or had too much) via numerous small-sized mid-day deliveries, etc.
Food trucks have most of the same issues as hotdog carts. If the rules are loosened, within a decade you'll see a rapid convergence of menu selection as a hand full of the successful owners now run back-of-house for everybody else.