I've been track racing 30+years (Since I was 9). In the USA and Europe. I think the real reason is we never had a "great" track racer. I know, Marty Nothstein. But Nothstein is a bit of a jerk and lacks the professionalism and "human interest" of Greg Lemond (shot in a hunting accident, returns to win TDF), or Lance (Cancer, duh.) Track racing is fun to watch, but the many varied events that make it fun to watch, make it confusing to understand for newbies. Also, everyone can relate to riding a bike on a road, up a hill, etc. But how many have been paced by a derny in a keirin, ridden three laps, only the last one of which they actually sprinted (Match Sprint), chased another guy on the opposite side of the track (Pursuit), grabbed a team mate by the butt or hand and throw them in the race (madison), etc.
The Lehiigh Valley Velodrome in Trexlertown PA has, bar none, the most successful track racing program in the USA. Development, big crowds (1,500 and up every Friday), sponsorship, attracts top racers, develops top racers, etc. But no one else in the USA has broken the code. By contrast in Australia, they have far more velodromes per capita and have several velodromes with great racing programs - as does Belgium, France, Germany & Holland.
Pat McDonaugh, who used to run the program at T-Town is now at USA Cycling to raise the standard of the track programs across the USA. Pat's a very capable, and proven. But I fear it's too big a project unless he's given the $upport he needs, and a good staff. The Australian cycling budget is 3X the USA Cycling budget.
In the end, it's up to us, the riders, to race at our velodromes, support them, and spread word of mouth every where we can how awesome it is as a spectator and participant.