The other side of the coin on why there are ramp fees, from the good old days.
A small private airport, could be anywhere. We landed, purely to practice landings at various size runways. The owner came out and asked us how many gallons we were going to buy. None. She informed us the profit on the gas paid for the runway, and every plane that used the runway owed her money, donation, or gas purchase. Which did we prefer? We filled up, and her gas was about the same price as our home field.
When the sale of avgas fell, and its price rose, people avoided buying it at airports with more amenities, so ramp fees became common at the large airports.
As more airports became more sophisticated in their pavement, lighting, and pilot amenities, the costs rose.
We all appreciate clean restrooms, comfortable chairs to take a break on, and a computer terminal with weather and capable of filing flight plans. In the good old days, the airport where I was training, there was exactly one bathroom, unisex, and used by the mechanics to scrub up after oil changes. The paper towel dispenser was empty more often than full, and there was no hot water. The good news? NO LANDING FEE and no required fuel purchase.
Most of the airports that I have used for long cross country flights waived the fee if you filled the tanks, so I rarely paid a ramp fee. Another quirk in the system to raise an impropriate amount from transients, was the high tie down fees. If I was staying for more than 5 days, I paid the monthly fee, as it was typically equal to 4 or 5 days at the day rate.
The reality is that few airports today make a profit, they are subsidized by some government entity, and that is why they can afford VASI's, ILS, long runways, and large paved parking areas for both planes and cars. 50 years ago, my home field did not plow snow, it simply issued a NOTAM and closed the field. Today, it starts plowing as soon as there is more than an inch, and continues until snow stops falling. Two always clean bathrooms, computer terminal with full range of weather and flight planning capability, pilots lounge with comfortable seating, and several pilot and plane owner related magazines provide a totally different facility from the "Good Old Days" that I remember. And a huge screen with all aircraft radar readouts, that you can zoom in or out to see what the traffic is in the immediate area, or out on the airways.
The runways is 3 times as wide as back then, and has lights. The taxiways are wider than the rinway was, ang we have instrument approaches that work, and are legal.
High ramp fee for a piston single are an abomination, but they are a product of the huge improvements in the airport facilities that are there for all planes that land.