Another primary consideration in introduction & eventual disappearance of Segmentata?

[Dan Howard]

Segmentata is munitions armour. It appears a couple of generations after lower classes started being admitted to the legions but were still required to purchase their own equipment (costs were deducted from their pay). Segmentata remains in use (along with hamata and squamata and musculata) until the state takes over the armour making fabricas. IMO this was part of the Diocletian reforms. During this time, segmentata only seems to have been worn by the lower classes - there isn't a single depiction of an officer or NCO wearing it.  After segmentata was phased out in the 4th century, the Empire underwent an extended period of success - both economically and militarily.

We see plate completely replace mail as the preferred armor when it entered production again in the Late Middle Ages, some 1,250 years after the Romans first produced it. Incidentally, it was the world's first and only Western superpower that used plate armor first.

Mail continued to be used along with plate in Europe for centuries. We have inventories and production orders demonstrating that mail often cost MORE than plate during this time. Plate started to spread when it did in medieval Europe because trip hammer mills and blast furnaces made it cheaper and faster to produce. This might help.
http://myarmoury.com/feature_mail.html

So plate became popular in medieval Europe for the same reason that it became popular in Rome: Economics.