Re:
Not read all the pages but isn't the decline as much to do with a shift in focus than anything else? None of the MTB media give more than a fleeting glance to XC so it's no surprise to see dwindling numbers. Downhill is also suffering. Try to get entry to an Enduro race though and you'll struggle.
Most new MTB's are focused around Enduro/Free Ride from 110mm travel up to 180mm so other disciplines are pushed to the fringes.