It isn't so much the amount of AVGAS used it's the bother of sending a full load of fuel out from the refinery and getting rid of the contents economically. This is the problem of supplying an aerodrome. Each semi holds up to 35000litres or more of product. The transport company gets paid cents per litre to deliver the stuff...if the run is either too long to empty a tank or too limited in capacity, its just plain uneconomical to make the delivery. Unless you can or two or three aerodromes in very close proximity can accept a single tanker at a time and get the truck back for another load of something else ASAP then the cents to not stack up...That and AVGAS gets transported in special neoprene sealed tankers that ONLY get used for AVGAS and there is the problem why drums and not tanks.
G100UL could change all that.