You need a lot of things for a gas station, a giant tank under ground, a run off collection system for the spilled gas/oil, they have to be covered these days, I’m sure most of this is just environmental regulations. You only see them in the grocery store parking lot if they have all of that, it’s not just a few pumps put up at existing parking spaces (well, maybe in Thailand).
I get a lot of gas in supermarket parking lots, several supermarket chains put gas stations in the parking lot of some stores.