Good to know. I've been in the Mt. Bike world for the past few decades and help support the local trail builders at work parties, learning a fair amount in the process.
In the Mt. Bike world they aren't that secretive, unless they are pirate trails because those cause problems. In fact they have amazing GPS apps like TrailForks that show you all the trails in your area with 5ft accuracy. I do know getting new trails built through the Forest Service and BLM can take 5-10 years, the more remote the trail the less likely it will be approved. A lot of the existing Mt. Bike trails were grandfathered in from the last few decades, with new trails much harder to get approval for. In the Mt. Bike world we are lucky as often times trail work parties are huge allowing us to keep the trails clean by fixing drainage issues, repair blown out trail, remove pirate features and block off areas of expanding trail footprint. When I Mt. Bike now I will stop on a trail and quickly move logs around to block things off or do minor trail repairs when it makes sense. I would suggest to anyone to do a few trail volunteer days, learn how trail builders see the trail so you can do little things to help maintain the trail when your out there - it doesn't take a lot of time.