It is supply and demand. More people with fewer sites per capita available. Not to mention the property cost/rent downtown versus a rural location
That last sentence is my point. Something changed.
In some rural places, it still is more expensive. Where located far from refineries, terminals, little traffic and little choices for other stations, it can be quite high. But those tend to extreme places, complete with the “last gas for 100 miles” sign, even if not true.
I haven’t experienced the reversal you speak of.