Just look at this: http://www.mlsplayers.org/files/April%201,%202014%20Salary%20Information%20-%20By%20Club.pdf and it becomes painfully obvious in a hurry why we suck on the world stage. I think I counted about a dozen players in the league who make seven figures, then it drops of dramatically.
Triple AAA baseball players make more money on average, and there's ZERO incentive for our best athletes to play this game past 2nd grade.
Listen, I'm a baseball/football guy 1st, but I don't think kids say in 5th grade "Hey I'm gonna quit soccer because I can only make 200K vs. 2 Million in football".
I get what you're saying, and I agree that it's not such a conscious decision. On the other hand, our very best athletes see WAY more football and basketball on television, sportscenter, etc. and many of them see it as their way out. It's not that we don't have the athletes in the USA to dominate this sport too, it's a function of how few of those athletes have any desire to develop soccer skills.
Guys soccer is about what's on your chest not what's in your wallet(World Cup wise)
No different than the Olympics, really. With that said, the teams with the highest aggregate salaried players tend to win the Basketball & Hockey in the Olympics, just like tends to be the case in the world cup.