Going through some of the AAA teams that have their rosters on Maxpreps, I only see a few obvious Asian names (not counting the kids that may be mixed).
I can't speak with 100% certainty why Asian / Indian kids don't play but some thoughts:
1. Asian parents may be a big influence. I know my mom discouraged me from even thinking of playing football. My school didn't have sports until my sophomore year and I wanted to pay freshman year. I heard you could play for your district school (Balboa) but my parents never did anything and I didn't know how to get connected as I was young.
2. At least in the Bay Area and LA / SoCal area, there is a strong contingent of youth Asian basketball clubs. Throw in all the AAU basketball teams around and you have kids who start and grow with basketball. I don't think Football is something many kids (at least in SF / Daly City) start off with.
3. Quick: Name an Asian-American NFL (or heck even college) football player? (Dat Nguyen comes to mind and Ed Wang who didn't last long). Ed Wang is a big of the exception as he was a big 6'5" 250 pound or so offensive lineman. Nguyen was 5'11". Point is that unless you're a QB / RB or WR, you probably aren't going to get a lot of attention. Hate to say, but having a role model helps sometime but those role models have to be visible. For those of you are either go to SI or familiar with the SI basketball program, there's this HUGE Asian kid that's probably 6'3" and at least 200 pounds. I watched him play when he was young and he was on the JV team last season (I think he was a sophomore but could be wrong). The kid likes basketball but I thought he could be on the football team. But don't see him on any rosters for football.
In basketball, you have Jeremy Lin, Yuta Watanabe (2 way guy from Memphis) and previously Yao Ming. In baseball, you've had Ichiro and a host of others who have played.
4. American football is strictly played in the states (unless you count the Canadian Football League). I don't know the exact number of non-American players but most of the talent originates in the states. The NFL tried the Euro League and there's a push into China with a football development program. If there was a push to develop American football in other countries, you could see more talent come in and people be more familiar with the sport. But at this point, Asian kids play basketball, badminton and volleyball (large volumes of Asian girls playing high school and club volleyball).