Oh enlightened one that is an extremely easy question, THEY EVOLVED. They went from 2 or 3 bay garages to multi use sites, most went into selling snacks, fast food, cigarettes, liquor, coffee, doughnuts all which have higher profit margins some went into oil change places. When you have higher margins on some sales you can afford to lower the margins on the bait (gas, diesel) kinda like having a sale but it's in effect 24/7/365. I started typing my response last night and spread out the typing over time as to give you a fighting chance to understand it better.
If a business needs a 20% return you can bet your ass that the business owner is gonna find a way to obtain it, that is why when the left raises taxes or requirements on a business the business responds and usually the response is to raise prices above what the actual costs are to the business.
The bottom line is that businesses do not pay tax the consumer does.