As most of us know, these 5 point harnesses are really strong. Much heavier than regular seat belts. In fact they're about as heavy as the ratchet straps we tie the cars down to the trailer with.
You'd think they really should be safe for 5 years.
They may be looking at a worst case scenario where the car is stored outside in direct sunlight but every car I know if sits in an enclosed trailer or a shop more than 90% of the time.
If they need to add UV protection or whatever,,, fine, but surely they should be able to make a set of belts that will last five years.