The trespassing laws for nearly every state are strikingly similar to PC 602. It applies also to OHV use on the very same private lands as it does for any other use of someone else's property. Yes, in most places, it's enforced, and the courts hand out appropriate penalties for violations. 3973 is not necessary for trespass laws to apply to OHV use. It applies to OHV use just exactly in the same way it applies to any other entry to private land.
So, I'll agree with you here.