MY TWO CENTS :   Tennis is suffering in the USA because there is a lack of real interest.  In other countries where tennis provides the opportunity for a better life, it is to their benefit for players to give a 100% commitment to their success on tour.  That is not the case in this country. There are too many other opportunities for a better life for most Americans; therefore, there is a somewhat blase attitude towards the sport.  If they give it a try and they don’t succeed, they can always do something else.  The “hunger” that drives so many tennis players from other countries is missing in American players, not all of them, but a large percentage.  You chose tennis because it’s fun, and because you have some talent, you initially do well; however, when the game starts to demand more of you, you quickly lose focus and interest.  The result, a lot of countries with a significantly smaller population than USA, have a higher ratio of players who are performing well on tour in comparison to the USA.