If anything I think it's getting more popular. More expensive as well. Maybe those other groups just grew up some and decided they didn't want to bike. Others may of moved. Maybe they found better trails. Biking is growing by the day due to gas prices. My LBS sells bikes left and right now.
Also, I agree, mountian biking is showing up a lot more on TV. It's only a matter of time before Hollywood makes a movie of it. lol