For a long time this sort of worked for both sides as the bathroom foot traffic would often buy some small item in the store and most items sold at gas stations have a hefty markup. Buying a Coke for $3 might net as much profit for the gas station as buying $30 of gas. Besides, the gas station can never tell if you're going to buy gas and just want to pee first.

Since the pandemic, a lot of gas stations summarily closed their bathrooms - even to customers. It sucks.