It's pretty clear that there has been mountain biking at a few ski resorts for a while, certainly long before 2011. My guess is that the process to get approval was more difficult than the process going forward that is based on the revisions to the law made in 2014.
I have an impression that early mountain biking trails were more for intermediate and advanced bikers. Providing rentals with lessons for beginners in order to build up interest means working to expand the potential market.
In a recent article about Whitefish, I noted that the first downhill-only mountain biking started in 2008. It was part of the effort to expand summer activities to keep from losing as much money during the off-season. Apparently still not making money, but the losses are smaller. The number of employees during the summer is half the number needed during the ski season.