And full ATC is expensive - but mandatory for an instrument approach...
Sorry for the stupid question, but why is that mandatory ? Several French NDB approaches are at non-towered airports. Regional ATC clearing you for the approach, "call us after landing" ?
...is heavily subsidized. Pool construction and maintenance are considerable (same order of magnitude of a small airfield, and more if you count staffing)
The reality is that you have to have a certain income to fly and the perception is that it is an activity for the well off.
That is very true. For the same reason a golf club is denied subsidies, even if it tries to minimise its fees for maximal membership numbers. On the other hand, by raising taxes, landing fees, training costs and EASA nonsense, flying being for the well off only becomes a self fulfilling prophecy.
How do people learn to land an aircraft properly when they have to pay for every landing?
A couple of airfields work with reasonable "annual fees"; A couple of airfields give discounts for students at a locally based flight school; A couple of municipal airfields in France are free.
In my country the above situation leads to problematic situations when experienced pilots want to practice and maintain their landing skills.