I think that it is precisely because in Europe manuals have been more popular that they have a predilection for SMG.
As Euros are used to and appreciate manuals, a much larger percentage of them will be tempted and convinced by the clutchless aspect of the SMG - it is being offered to them (packaging) as a manual without a clutch.
In NA, those of us who want manuals (we know who we are) have already made a choice NOT to get auto (which is default here as it were). The way the packaging of the SMG here is would force us to make a choice of giving in to a kind of automatic. The message here, that the SMG is a manual without a clutch is not clear, the sales guys mutter ''Oh yeah it is like an automatic but you can really shift on your own''....they do not have a clear positioning.
So since the manual driver in Europe is not, by definition, necessarily an enthusiast (even those who get the M5), but rather someone who drove manuals all their lives and appreciates them (nothing more) the Smg is an easier sell there. Here, we enthusiast define ourselves in part by the fact that we are ''hard core'' because we are mannual drivers and are therefore more conservative/resistant to change. I know that I am generalizing and that there are enthusiasts who do not drive manual etc. but you get my gist.