As a result of the proximity of the major cities and the high urban density, there are not the same requirements on general aviation as there are in countries that are vast such as the US or Aus / NZ.
Have you looked at an atlas recently. New Zealand is about the same size and the UK with a population 15 times smaller than the UK and you say there is a greater GA requirement here than the UK. I find that hard to believe.
Sure private flying is much much more affordable here but that's because it's made stupidly expensive in the UK, mainly I suspect to try and keep out the ordinary person.