Seen some of the back and forth, and a few things to add to what has been said above
I have heard this as well, but I don't agree with it as all and think it is just an easy stigma to associate. Its not a work ethic issue it is an availability of sport issue. The core sports of Baseball, Football, Basketball, and now Lacrosse are well supported locally, and financed mostly through the High Schools themselves. These sports have their overseeing body issues as well, but for the kid wanting to get into a sport those sports are highly competitive locally, highly promoted, and have lots of money backing them. Hell, look at the little league baseball World Series, it makes the ESPN highlights and telecasts! It's absolutely boring to watch, but it's got the money backing to promote it. Tennis is like this in many other countries, which puts American players at a disadvantage. Prior to the 1990's tennis enjoyed a boom and thus there were many players out there in American tennis, but between the ATP, ITF, USTA, and other associations much of the opportunity has been squashed, facilitated by a rise in foreign players to the sport. Former Soviet states had a influx of people turning to tennis with less regulated systems that allowed for growth. And now Asia has gotten into the tennis market so their players are starting to make their mark. At this point the US market has just fallen behind, and will probably never be as dominant as it once was.
Tennis is an amazing sport, and suits potential athletes who thrive in an individual athletic sport. But if you are a top Athlete, why would you go into a sport where less then 100 players in the world make any sort of living? And a small one at that, traveling around the world grinding it out in Challenger tournaments? 4000 professional baseball players do much better without having to leave the US. And for scholarships, those just don't exist in tennis to make it worthwhile. Many reasons for this, but it stunts the growth of Jr' players who would give it a shot.
Lots of great ideas out there and now some players speaking out. Many people are speaking out against the USTA and their programs. And the Elephant in the room is the Gambling industry, which the ITF is now beholden to. This arrangement is affecting the ATP/WTA, with all the different country associations trying to get their piece of it. This includes the ITA, which is why you see things like 1 set doubles and no-ad scoring. For the US, scholarships dedicated to the sport would help, but if local coaches and academies are given more freedom to train and coach the local kids, run tournaments, and create better localized competition it would create a vast network of American players. More American players in the top would drive more fans out, no doubt about it. I have always felt that High School tennis could take over some of the tournament organizing from the USTA, and that programs bridging Jr players to life after Jr and college tennis would go along way to helping good players stick with the sport. There is a generation of players from age 18-35 that have no idea how to stay involved with tennis, and in many cases just disappear from the sport altogether.
I have always thought that a system where players play individually, but play for an organized sponsorship team, similar to like NASCAR, might be a good way to go to promote events and organize their time. This is sort of what was happening with the WTA and Grand Prix of the 70's early 80's, and really drove a lot of the local fan fare and pro tournaments. But I don't see the ATP or anyone ever giving up their stake in this, so it is what it is...No fans at events, and all the money coming from gambling. Its depressing to see this happen.