But surely most people who can afford a $2000 bike also live near a park? So they can throw the bike in their SUV and drive to the trails?
I live in a place where trails are just a bike away. I was a competitive XC MTB guy before switching fully to road bike. I also used my MTB to go to various places and train in paved hills or mountains. Then I bought a road bike and was planning to just use it for road work and do trails on MTB. But then, road biking is much more fun in paved roads and much faster that I gave up my MTB and sold it to buy a nice Chiner frame.
Well the thing is, I understand why road biking is more popular than MTB. Lot of people just want to go from point A to point B using bike and the fastest way to do it is on a road bike.
Maybe another thing is, road bike races are much more exciting to watch than XC MTB. On road bike race, you need to factor in a lot of things and there's a team work and there's a lot of strong riders on the field and is not just dominated by one person. Meanwhile, on XC MTB, I know only 2 people who is really strong they dominated XC MTB for a decade each and that was Julien Absalon and Nino Schurter. On XC MTB races, the one who goes first on single track is usually the winner and casual riders don't want to watch a single guy riding solo on a breakaway.
This is just my opinion :p