But makes the world itself a lot more boring.
The point with having onlyu categories instead of specific armors is that you can then assign relevant specific armors into the different categories, depending on the setting.
Consider Europe around 1100, 1250, and 1400, and 1550 BC
At 1100 AD, light armor is a chain shirt, medium armor is a chainmail hauberk with pot helmet, and heavy armor is a mail shirt, arms, gloves, leggings, coif and a barrel helm, possibly reinforced with plates at knees and armpits.
At 1250 AD, light armor is still a chain shirt, medium armor is chain jacket and pants with metal greaves and vambraces and a bascinet, heavy armor is plate over mail, with the late being separate peices but covering most of the body.
In AD 1400, light armor is a front-only curirass, medium armor is cuirass with conquistador helmet or bascinet and partial leg and arm plates, and heavy armor is full plate.
In A1550, light armor is quite likely again a chain shirt, but this time around fine enough to wear under clothing, medium armor is a front-only breastplate and helm with armored gloves and heavy riding boots, and heavy armor is thick plate half-armor with full helmet.
By having the game describe armor only as light, medium, and heavy we save ourselves the specifics of these different kinds of armor; the exact descriptions become setting details while the game effects remain the same for each category.