It's an extremely good question...
Greece - arguably the one country with the best economic case for GA, ss well as the best weather - has only about 200-300 PPLs. They are pretty active - far more active than the UK bunch - but there aren't many of them!
I think UK and Germany and France have loads because of historic factors going back to WW1.
Elsewhere, GA has had to fight a bit. Europe is not about individual freedom like the USA is. As a default position, Europe is basically a socialist State and thus personal freedom is an unwelcome concept.
And until ~ 20 years ago much of Europe was a military dictatorship - like most of the 3rd World.