Mail replaced segmentata? Why?

[Tarbicus]

There is another possibility - the Romans simply forgot how to make decent plate.

Except that helmets and shield bosses were still common, and both use pieces of plate no smaller than needed for a lorica. Not to mention the common household cookpot.

But was it hammered? Are we so sure of it that there is no possibility it was rolled steel? Do helmets, cookpots, etc, show the same evidence of forge welded (I think) layers to make the complete plate as seen in examined armour?