There were two issues with the Explorer incidents.
Ford couldn’t get the Explorer to handle properly so they keep lowering and lowering the rear pressure against Firestone’s suggestion. The final pressure was like 22 psi (way too low for a vehicle of that size).
I got this from a less reliable hear say source: Firestone left out a component in the tire that was identified on the DOT code. Basically the lied about or changed how the tire was made from the initial pass on the DOT test.
In southern climates w/ heat + the ridiculously low pressure Ford was trying to run = fail.