There are 3 issues--1) finding exactly what they did wrong, 2) the prison sentence length even if they did all they were accused of, and 3) the whole concept of national parks. Speaking to the third issue,
When park boundaries are drawn, anyone living on the park is paid to leave. Years later, population growth spreads farmers and ranchers right up to the boundaries. After more years of economic expansion, they want to lease a little land on the other side of the boundary. (The Hammonds of Oregon paid their rent, unlike the Bundies of California who want Federal land to use for free.) After more years, they think like owners because no one else is ever there, and resent the rare interference from outsiders who don't know the parcel intimately as they do. After more years, if they use controlled fires on their own property, they use them on the leased property, too.
As the U.S. population doubles and doubles again, this pressure will increase. It'll be like in Africa, where the hungry population is bumping up against preserves of large animals and poaching them. What's the long-term answer? It will be either to 1) condense national parks into little spots that even ranchers don't want, or 2) build Trump fences around the parks with armed guards. No borders, no nation. Hire MinuteMen. They usually hang around the Mexican border, but appeared up here a few years ago watching the Canadian border. So the guys occupying the park right now, can continue living there, paid by the government as the park's border patrol to keep out illegals like white ranchers. It'll happen in a few decades anyway. Just do it now and both sides will be happy. This whole problem is just a timing difference about when to do the inevitable. This genius is why I should rule the world.