The same thing happens here. The trail maintenance groups go in and sanitize the trail. In some cases, it is great in that they make the trail sustainable, and control erosion problems. In others they turn some tricky, fun singletrack into what might as well be a paved path.
I find myself leaving my MTB at home more often in favour of my cyclocross bike. It is the only way I can make some of these trails challenging for myself.