Because you don't want you to be stuck with a mattress that isn't right for you
Mattress failure refers to the physical state of the mattress. It does not refer to the customer's opinion of whether or not the mattress has failed for them.
This is when the cell walls in the foam collapse to a point that the mattress changes shape. A refund from Mattress failure will not occur unless there is a dip/sag in the top of the mattress of 20mm or more.
Springs that break through the material or broken springs inside the mattress.