Hi,
In places where "industry" and "commerce" rules, it's hard to appreciate different music, is how I think of it. Even in the history of progressive and experimental music, that area in the north was very active, and had a lot of very nice stuff.
The countries with smaller numbers, btw, are also the countries (these days) that respect "artists' the least, because of their commercialization. In places where some folks are appreciated, they are likely to live out a bit more and play ... but how can you make it France with a metal band, when the only thing they like is stuff that both you and I go around saying ... is that supposed to be music? ... and sometimes they call it some kind of jazz, or RIO or some other copycat idea!
England has a very diverse bunch of scenes and this would help dilute the number of "metal" bands, and if you did a similar map for "folk/folk-rock", I think you might find England on top of the idea. France would likely win the jazz sweepstakes ... it changes/vibrates differently every year for every country! In Greece, it's probably because it has the best chance to sell right now, in a horrible economic time ... can you imagine a band trying to play jazz in Greece? ... people going ... what's that? Well, there's always Zorba dancing in the beach!!!! Gotta call that something!