A possible factor: it's not so much that there are more or less bands in Europe or the US, but it's probably a hell of a lot cheaper to get around in Europe - at least for the fans; I don't know about the bands. You have a ton of established, well-known venues all over western Europe, even just within the countries which are on par with US states in size. Having recently been to the Netherlands, I'll use that as an example: there are at least three places in Amsterdam alone, Boerderij is about 30-40m south, that place in Belgium another hour away or so, PPEu is about three hours away by the German border, and I know there's several other venues/festivals scattered around a country that's about twice the size of New Jersey. There's ALWAYS shows happening every few weeks or months, and it's relatively easy to get to most of the venues by car or by public transportation (there was a train stop right next to Boerderij, where we saw Damian Wilson + Friends.) Even Germany has a shitload of shows within a couple of hours of each other, and it's a considerably larger country at nearly the size of Montana.
Contrast that to the East Coast, where most of the shows seem to hit. You have Jaxx in VA, the Troc over two hours north and then a couple of NJ and NYC venues 4-6 hours from there (Jaxx), a couple places in MA and CT... if you go south from Jaxx there isn't anything until you get to Raleigh, Charlotte, and Atlanta (except maybe Norfolk/VA Beach, but it's out of the way.) There's a House of Blues in Myrtle Beach, but it's also out of the way. You have to travel a good 1000-1500 miles to get the same number of possibilities as you have in one small country, and if you don't have a car (or a friend with one), you can't get to many of those venues.
So while I wouldn't say Europe has more bands, it's a MUCH friendlier touring environment.
Contrast that to the East Coast, where most of the shows seem to hit. You have Jaxx in VA, the Troc over two hours north and then a couple of NJ and NYC venues 4-6 hours from there (Jaxx), a couple places in MA and CT... if you go south from Jaxx there isn't anything until you get to Raleigh, Charlotte, and Atlanta (except maybe Norfolk/VA Beach, but it's out of the way.) There's a House of Blues in Myrtle Beach, but it's also out of the way. You have to travel a good 1000-1500 miles to get the same number of possibilities as you have in one small country, and if you don't have a car (or a friend with one), you can't get to many of those venues.
So while I wouldn't say Europe has more bands, it's a MUCH friendlier touring environment.