AFAIK DeLorean's are not cold rolled steel. CyperTrucks 1.4-1.8mm 1018 cold rolled versus 0.8mm 304 DeLorean. The thinner steel on the DeLorean makes is easier to work with enabling larger panels which need fewer flanges. It seems the theory as to why the panels are so thick is that they do provide some structural stiffness.

The early prototypes had 3mm thick panels so it's likely some design decisions were left over form that.