None of them would ever drop out of the draft
This year there will be way more Americans.
The International system is just different Their leagues are tiered and they start kids up the way we would in high school. Some kids declare just to get out of their situations though, because they do players dirty sometimes.
Also with the international game it is cyclical. They were pumping out great players in the late 90s and early 2000s. Then for almost 10 years they didn't produce shyt and now the cycle has started again.
But in the end the americans will always produce more players in the draft (who actually play in the nba over a 10 year period). For as many folks overseas that play basketball they just don't have the funds, genetics and pool of people that america has when it comes to who is playing in the NBA.
Also we can't compare a american kid to some euro wno has been playing professional since he was 14 and who basically only went to high school to learn how to play basketball.