Cheers all. Here's the back story; it's a fascinating and great read, even if your not a mountain biker.
https://www.pinkbike.com/news/banned-in-the-usa-part-1-2016.html
https://www.pinkbike.com/news/banned-in-the-usa-part-2-2016.html
https://www.pinkbike.com/news/banned-in-the-usa-part-3-2016.html
Just thinking that hiking up a trail that a bike is flying down, could be hazardous to one's health, and that might be the main reason behind the early thrust.