European aviation is insanely expensive. There's no such thing in Europe as economy in aviation.
Setting aside European aviation, in the real world, the 172 is very economical to operate.
O yes there is such a thing as "aviation economy" in most European countries; only it is measured on a scale different from yours. I'd almost say the reverse is true: it is the USA with its very cheap fuel (where in the world is AVGAS cheaper?) and abundance of public aerodromes that has no real sense of economy.
Actually I think these words narrow-minded, typically us'an in this respect, to consider the USA "the real world" as regards private flying. You really believe European countries are the exception? Most places in the world have scarcely any private flying, either for poverty (like most African countries, and a good deal of Eastern Europe) or because it is, or was until recently, expressly forbidden, like in most socialist/communist countries. Is the USA the real world? For private flying it isn't, it is an exceptionally nice place. Western Europe is still on the better side, I believe. Certainly closer to average than your nice USA.
NB do be aware that one can't really speak of Europe as a whole in this respect. Despite all the political showtalk, differences between European countries are huge, even if they are in the European Union as most are now. France is quite G/A friendly as Europe goes, the UK much less.
Caveat: only in a nice place like the USA, where cost of operation is very low anyway, can the OVERALL cost of owning and flying a C172 be low. Where operation is cheap, acquisition is a greater part of the total cost; and I never denied the low price of second-hand spamcans these days. I still keep up that the C172 is (for a 4-seater of modest capacity and performance) not particularly economical to operate. I will grant you that in several places it may be a very good overall compromise, due to the large offer and associated low purchase price.
PS one aspect that I did not mention, for lack of information, is maintenance. I am willing to believe the C172 is cheap to keep up to standards, probably cheaper than comparable planes due to its vast numbers; but I suspect that again it will be cheaper in the USA than in most European countries.