M14P is right.
Although there is a profit margin on AVGAS sales, in the volume that you sell to GA it doesn't go anywhere near meeting the costs of running a licensed airfield. In a country where GA is regulated to the point of extinction and receives no subsidy from the taxpayer, landing fees are the only way the GA Airfields can survive.
QNH1013
You'll need to buy a hell of a lot of fuel/ oil and eat all the cakes in the cafe to pay the salaries of the Controller who cleared you to land, the 2 fireman who would have rescued you in an accident, the guy who served your fuel, and the lady in the cafe who made your tea!
Most GA airfields are small businesses with very small margins, we certainly don't need anymore disappearing under new housing development!