promote the sport to beginners
I've been riding for about a year or shall I say I've riden about 15 times on single track trail. Never before have I riden on such tricky trails. The sport needs to do more to support rookies to the sport right down to the basics the framework. Most clinics are geared to beginners/intermediates everybody's definition is different. Snow skiing ofers great beginner classes, mt biking should createa basic beginner session.
While I think you're right in that it is difficult to begin biking on your own, you should consider the roots of mountain biking. It started as a bunch of guys going out, experimenting, riding alone. It was a very individualistic sport back then, and it has continued to be so today. Sure, you get groups of people who ride together, but it's just not as organized as skiing. There are no set times for the trails to open, no one patrolling (for the most part), no tickets to pay, etc.
I would recommend what bikers have done for decades: school newbies yourself. Volunteer to take someone out and teach them a few tricks to get them going. Get a group of beginners together for weekly rides.
Not sure where you live, but you may want to do some digging around to find stuff on beginner clinics/rides/etc.
Over the past couple of weeks here, the store I work at parttime has hosted two beginner clinics. We also host two basic maintenance clinics. There are several fee based beginner clinics taught through the parks & recreation department. My alma mater offers beginning mountain biking classes.
I'm sure the same can be said for other locales around the country. You just have to look for it.
A year ago I started a Yahoo! Group dedicated to beginners/newbs and folks that are in general just slower than everyone else. The success of my group rides has been hit and miss since it's existance.