The vast majority is flight training, fulfilling currency requirements and commercial operations (135 charter ops, survey and similar, fire fighting, etc.)
Most of the pushback against lead free fuel is actually from the commercial operators that consume the vast majority of the fuel and operate higher compression engines that need the octane boost normally obtained with lead. The recreational side could have switched ages ago if not for the shared infrastructure. The recreational part 91 side is already increasingly using automotive gasoline through newer engines (rotax 91x series), increasingly common EAB airframes and mogas STCs. Given that auto gas is half the price in most areas, the cost sensitive recreational market has already been moving in that direction.
These stats sorta disprove the OPs comment, but I think these stats kinda bury how a lot of personal flight time is also for currency and flight training, as a lot of pilots schedule personal trips to maintain their currency.
Also to note is that a lot of General Aviation is a pipeline for airline pilots and in countries where there is not such a strong general aviation industry there are higher accident rates.
Most of the pushback against lead free fuel is actually from the commercial operators that consume the vast majority of the fuel and operate higher compression engines that need the octane boost normally obtained with lead. The recreational side could have switched ages ago if not for the shared infrastructure. The recreational part 91 side is already increasingly using automotive gasoline through newer engines (rotax 91x series), increasingly common EAB airframes and mogas STCs. Given that auto gas is half the price in most areas, the cost sensitive recreational market has already been moving in that direction.