500-600 lbs ATV with what looks to be a three or four inch strap per wheel is while over the securement requirement for MOT/DOT.
This is the way the car haulers tie down their loads. I would want a backing plate on the underside of the deck using bolts/washers/lock washers and Nylon nuts...... NOT Lag bolts into the wood. There are straps designed to go over tires, they would be more secure.
There is nothing really wrong with the system, but just like must "Consumer" grade stuff the designers and manufacturers never put in those extra minutes of thought. Or maybe it's the accountants that screw it up, crying over a couple extra dollars cost per unit.