Maybe I used to ride at a different time but the trails I always mountain biked were primarily hiking trails that mountain bikes took to. (Case Mt in CT, etc). So most of my riding was done on hiking trails. As far as I know there was no dedicated mountain bike maintenance team and as a result there weren't really specific MT bike features either (log rides, banked turns, or whatever).
The only trail maintenance I saw that I considered critical was erosion control and that was normally done by hikers on the trail or park officers at most places I used to ride.
My guess is that was more in the hayday of mountain biking and now mt bikers want trails that ride faster, with more features, to improve their ride, and in that case I can understand unsanctioned trail maintenance crews. It would seem stupid to me to have someone bitch about a "trail boss" who is only improving the riding conditions of a particular trail (or creating a brand new trail).