Annoying maybe, but not so awful. There's a lot worse things they could be doing.
It may be a situation of what I call the "fun police". Some people just hate to see anyone else enjoying life.
I don't know what his plan is. Say some 15 year old kid gets home from school and goes for a ride rather than sitting around texting and playing video games like many of the mindless youth these days. Then he gets pulled over by the Sheriff on this guy's land. What next? The guy going to press charges against this 15 year old who most likely didn't even know he wasn't welcome on the property?
Say crossing the land was the only way for the youth to get from his house to the legal snowmobile trails around here. Once on the trails he would go ride for hours and only cross this guy's land on his way home. Now this fellow creates a situation where this youth can no longer ride at all because he doesn't have a way to trailer his snowmobile to the trail head. How sad is that? And it does happen....I've seen it.
I don't know the situation...its all speculation. But given the comment about stopping people riding in a park....I'm betting its the "fun police" scenario.