It's the Law—Required Equipment
Before an ORV may be operated on any property, the operator is responsible for ensuring that the vehicle and its riders have the required equipment.
For Operators and Passengers
ORV operators and all passengers must wear a U.S. Department of Transportation–approved crash helmet and protective eyewear or goggles except when the ORV is equipped with an approved roof and the operator and passengers are wearing properly adjusted and fastened safety belts.
This was copied right from the DNR's ORV handbook. I don't agree with it but its the way the law is.
Seems like I read some where that they are trying to change it for private property, if work is being preformed.
Hope this answers your question.