Back in the ancient past when I did subdivision work, easements weren't just contracts - they were property. Ask a lawyer. They provide limited rights to use the land, and once granted those limits can't be changed without something of value changing hands.

Of course, as applied to NWP - maybe the trail people, in the long run, would be better off hiring some land lawyers to figure it out and support actually buying things where needed. That's how most conservancies work, and they pick their battles carefully because they usually don't have a ton of money to waste. It doesn't make as many headlines as suing everybody in sight, but is often more productive.