You'd have to do some search for specific laws, but the idea is that small cylinders, I think up to 1 lb can be transported and used with minimal safety regulations.
When you have bigger cylinder, who can be lethal when something goes wrong- they require separate and vented compartment.
I noticed lately that lot of restaurant no longer use gas hook-ups, but they use portable stoves with those cup-sized cylinders.
My guess is that there have been too many restaurants fires and small cylinders make more sense safety-wise , even with extra cost.
Our son took us to Korean restaurant where food was cooked on our table. I sure would not like to have big propane cylinder on my table.
