Because food poisoning kills and veggies carry risks as well. We at least pretend with health inspectors to make sure places are safe but there would be no way to inspect someone's home to see if it is safe. The short story is that shitty people trying to make a quick buck ruined it for everyone. You can how ever operate out of a co-op commercial kitchen, even food trucks depending on the type have to rent a kitchen somewhere to make certain foods they sell and keep warm in the truck.