Why cant I use ratchet straps for tie downs????

As the camper rocks from side to side a lot of stress is placed on the tie-down anchors (on the camper)
The straps don't have any give like a spring loaded tie-down . A strap can damage the anchor. I have seen tight tie-downs do a lot of damage to a campers anchors when made too tight.
If you use a strap and a spring then you have to make sure the hook will stay in place and not fall off when it flexes.
If you look on the Tork-lift website, they explain how to make the tie-downs just snug.