Nothing agaisnt Gamma here, it's just marketing. Gamma strings are made by Toa and the same strings are available through different brands and distributers who are more actively present on the European market. We get back to the importance of marketing, for strings to have huge volume sales they have to be supported by massive marketing and be widely and efficiently distributed through retail outlets.
Both of these go together, Gamma has not achieved the notoriety that they have in the States simply because the market is already dominated by mostly European brands, but also the big racquet companies. It is not evident that the huge investment to increase the market share here would be a profitable venture. That's up to Gamma, but you are right, they do have good strings. I personally think that there are other strings on the market which are probably more interesting, but that's another story.
Bye for now,