Do you seriously think to yourself I need fifteen quids worth of petrol ? Over the last 35 years I have always filled my tank and then I go back when it needs refilling. Perfectly normal and that really isn’t causing the problem. Keeps me out of the queues. I would hazard a guess that the problem is coming from people queuing who are buying small amounts of petrol which means less staggered purchases.
Firstly it's rather arrogant to think that everyone can afford to fill their tank each time and secondly, it's not actually good for your fuel consumption to have a full tank.