I believe the following list is factual, but I'm sure I missed some items.
Airport landing fees, FBO 'handling' fees, ATC fees, avgas 250% higher (tax included), fees to create and issue initial pilot licenses, fees for renewal of limited period pilot licenses and ratings, mandatory "differences training" sign-off for any aircraft type (whether reasonable/not and with instructor), no learning to fly in your own privately-owned aircraft, no independent flight instructors, flight training companies licensed with fees paid, archaic and complex training for IFR rating, 20% sales tax applied to every item bought and every service purchased in relation to flying - including flight instruction and mechanic's labor, no independent mechanics, workshops licensed and fees paid by maintenance companies, complex maintenance paperwork processes involving multiple parties - 4 x price for annual inspections including annual taxation/fees once the work is done, no A&P mechanic inspections allowed for parts airworthiness - parts must come with paperwork (often precluding used parts), aircraft manufacturer advisory service bulletins made mandatory plus they must be performed by licensed mechanic.
It seems to vary a little country-to-country, but not a lot.
I think most of the additional expense results from government minimizing its aviation related costs and maximizing its revenue per operation, versus providing a service or enhancing safety. Reduced economies of scale compound the direct impact of the above.
Additionally, European governments just like to suck up far more money to waste. All taxes are much higher, not just aviation costs. It's a pretty sick place, frankly! If you thought US politicians and bureaucrats could screw things up, you should take a look at Europe!