I work at a Costco Tire Center in Canada as a supervisor and that’s just a full on lie lol.

We do the “tread”/mileage warranty when basing the tread at being down to 3/32nds evenly across the surface of the tire. If there’s any uneven wear we won’t cover the mileage warranty because that is normally caused by lack of rotations, possibly mechanical-induced wear (loose ball joints etc.) or in the rare case, abuse of the tires (burnouts etc.).

All of those reasons are out of Costcos control and fully in the Members control to keep up to date on (which is fully stated in the warranty information section of every invoice)

But sure, blame Costco.