Short answer, because there is no real regulation on aftermarket products. Any company can do their own tests and it works great. However, most of these tests are done independently and not approved by the manufacturers of the seat. You do have some manufacturers who produce their own products that are approved and tested with their seat. It is a simple reading of the manual, phone call, or emails away to find out what they allow. Rule of thumb, if it did not come with the seat in the original box, it is not tested or approved with the seat.