I really can't understand this argument.
First, the USA leads the medals charts of every Olympics games. They are able to develop a lot of great athletes in a lot of different disciplines. How is it that they the swimmers don't gravitate toward the NFL, NBA or MLB? And the gymnast? And athletes? How is it that the USA can develop the best sportsmen and women in so much different sports, which are all very low profile in comparison with Basketball, Hockey and even Tennis?
Second, why would the europeans and south-americans best athletes gravitate toward tennis instead of their own national higher profile sports? Why would it be different for the Europeans than for the Americans? How high profile do you think tennis is in Switzerland, Serbia, Spain? Especially before Federer, Nadal and Djokovic?
America has the biggest population, the biggest financial means, probably the best infrastructure, probably one of the best "know how" in developing sport people. For some reasons, it doesn't work for tennis. And these reasons are more likely a problem inside the american tennis than the problem of the tennis relative to other more desirable sports.
America differ from European countries on its teaching policy of tennismens. It doesn't differ from them on the importance of tennis relative to others sports.