Mark, I feel your frustration. I see it everywhere. At Lew Mo it's particularly frustrating as I tend to the trails there. This past weekend I noticed a new line next to the right of a tree when the established trail is CLEARLY to the left and has been for years. The new line wasn't there the weekend before. This wasn't a "going too fast so I got lazy" development, it was "oh, a couple of roots to the left...never mind that I'm riding a bike that's designed to handle the rough stuff...let me just ride to the right instead 'coz it's smoother"
We learned from IMBA TCC Training that one way to get a trail to stay as originally designed/built is to place visual cues that guide riders (somewhat subconsciously) in the right direction. Often, if the new line is burned in too much, it becomes the "new normal" and hard to correct, but when you see a newish line forming that isn't right, addressing it right away can help. A few largish branches and/or rocks strategically placed, along with a dusting of leaves from the forest floor ("dressing" as IMBA calls it) can make it "disappear" for all intents and purposes. It's not perfect, but I've used this technique at CR, 6MR, Lew Mo, KVSP and countless other parks and have found 9/10 times it "sticks" (poor pun)
Only takes a few minutes out of one's ride, too.