Unfortunately, my understanding is that most of the leases were renewed in the 90s and mid-2000s. I believe they are 30-year leases. I'm finding that out.
There's a difference, however, between their long-term leases and their yearly winter-operating plans. Their operating plans are subject to change and can address such issues. The sense I've gotten from the Forest Service is that they're receptive to this issue.
In certain places it may be that the ski area is already cool with it as long as everybody is chill. But management changes, and, as we just saw with the Jakes parking issue, having a concrete (heh) long-term solution, rather than relying on informal ad-hoc "this is how it's always been" approaches, is probably the better way to go. For example, I seem to recall that Kirkwood used to not care, and then started to tell people to leave after Vail bought the area. But I don't ski that area regularly (once or twice a winter at most), so I'm not that familiar with the issues there.
At this point, I'm basically in information-gathering mode. I want to have a more complete view of the issue before deciding what the best approach is, and where (we're talking several different forest management units with different staffs). And, yes, all the other points you make are well-taken. But there's definitely been a good amount of arbitrariness about barring public access beyond the obvious legitimate concerns about people skinning under patrol running A/C.
Edit to add: I should note that I have no idea how successfully such an effort might be, but I think it's worth trying. And, as far as I know, nobody has pushed back on the issue in any comprehensive manner anywhere else in the country. Winter Wildlands tried to get something into the Ski Area Enhancement Act a couple years back, but nothing came of it. There's a few places that have formal policies (e.g. Crested Butte comes to mind), but not many. Sugar Bowl does as well, but as I stated above, they've been something of a disappointment to me. Well-intentioned, though. I'll give them that.