here are some reasons:
1---kids in the US learn baseball and basketball at a MUCH earlier age than tennis; then as they get older, there's a natural tendency to move toward sports with which they are more familiar.
2---the sports pages don't cover tennis; the local public doesn't attend high school tennis events, while the local football and basketball games are the most attended stuff the HS puts on. If you're a kid and you want adulation and peer respect, tennis ain't the way to get any.
3---tennis is perceived as a sissy sport played by the inept. Credit Bill Tilden's activities for this.
4---US television promotes the heck out of football and basketball and baseball (these consume plenty of hours of air time). These bring big ad revenue to the networks.
5---tennis takes too long to learn. There's a distinct lack of immediate gratification. The US is a self-indulgent nation, so immediate gratification counts for very much.
6---team sports provide identity and rewards/prizes/trophies.
7---the established pro teams pay lots of money in baseball, basketball, hockey and football.
8---coaching for the Major Sports comes pretty much free, via local park districts, etc., and volunteering parents. This works well for team sports, but not very well at all for individual sports, so individual sports suffer.
9---you can't hit the other guy in tennis.
I'd like to add to this if I may.
1 - Guys like Agassi was starting tennis before he could even walk, so I don't think that's always the case. However, kids are mostly social creatures, and football, and basketball allow them to have more fun being social.
2 - True, the only people who appreciate tennis accomplishments are usually those who are interested in Tennis. The tendency for a tennis players to be interested in another sports news, is a WHOLE LOT MORE greater than, say a basketball player interested in a tennis players accomplishments.
3 - Don't know about this, I think a lot of people just don't care either way.
4-9, all true.
Also, one has to consider the cost of development in playing tennis. I'll compare it to my high school days. On the tennis team, I had to pay for my own rackets (strings, overgrip, bags, etc.), shoes, clothing. Also, in order to get better as a tennis player, I also had pay for tournaments, and in Hawaii, if I wanted to pay a national tournament, that also meant paying for airfare, and hotel. So suffice to say, I didn't play national tournaments, and was relegated to playing the people in Hawaii, which is basically like playing in the league. There's just a certain level of competition needed to get better, which wasn't there.
Now let's take my basketball team experience. I paid for shoes, and my own basketball. Uniforms was provided. I wasn't good enough to even consider going to national camps. There were some guys on my team who went on to play college ball (Div 1, Div 2, JC).
My point is, Tennis, is inherently a much more expensive sport to play and excel in, while sports like football, and basketball are not, and there are a lot of athletes in basketball, and football, who probably could have excelled if given the opportunity, however, the costs prohibited them from doing so.