[kronckew]

Plate armour evolved from integrating little plates into chain mail, or making armour with overlapping scales or lamellae, then Brigandines made with small but easily made plates. Fabricating large pieces of consistent High Carbon steel into large shaped plates, and heat treating them came last.

It is very expensive and time-consuming to make and fit a suit of full plate and keep it not only light enough to wear, and flexible enough to fight in, while not letting those pesky Welsh/English rostbifs poking arrows though it into your expensive flesh.

Mail, scale, lamella armour, and brigandines are easier to make and fit. - and don't require as much work to adjust as you get older and put on a pound or two. And are good enough for the Hoi Polloi and peasants. (And even lower status knights and men at arms.)

Mail is boring to make, drawing wire, winding it on a mandrel and cutting it into rings, or punching washers for 1/5 of the rings, flattening the cut wire ends or the whole ring, and punching the ends for rivets, then assembling in mind-numbing regularity while carefully riveting the ends closed is a job for the slaves, in any case, or at least the peons. Good plate takes more skill and expertise. Only the very richest and most politically powerful could afford full articulated and highly decorated plate proof against longbow, crossbow, and sword/axe and lance.

But not against some slovenly low class smelly peasant hooking you off your expensive horse, knocking you on your back and poking a cheap ballock dagger thru your eye slit.