I think this is partly because flying is so expensive in Europe and as a results pilot tend to have a lot less experience. It's really a hobby thing only. Not a "Hey I have a business meeting in Hamburg, let's take my Cessna" thing. The EASA/JAR tends to be very strict on the commercial thing so even taking a colleague on board a private plane to a business meeting would count as commercial use and thus require a CPL (in fact I wouldn't be surprised if flying yourself to a business meeting would count as commercial!)

Part of this is because of the strict regulation. Most pilots only do VFR because getting IFR rated is so expensive and not really interesting from a hobby perspective (no nice views, you can get the same experience in a simulator). Some would do special VFR but it's generally frowned upon.

Also, GA aircraft are generally not welcome at major airports unlike in the US where airport access seems to be viewed more as a right than a favour. So the processes around them tend to not be understood very well. This is another reason nobody opts for IFR ratings, there's not much you can actually do with it anyway, they're not going to let you land at Amsterdam with a Cessna 172 :P They definitely wouldn't carry avgas either.

So, basically we have a whole continent full of "sunday pilots" in terms of GA. And I think the strong legislation and thus costs are part of the cause for that.

PS I've never flown in or even visited the US so perhaps my understanding of the GA landscape there is wrong. But AFAIK it's really used for personal transportation there, which is kinda cool IMO.