Hi there, while there's always more room for answers, perhaps these older posts about lorica segmentata will get you started:
https://www.reddit.com/r/AskHistorians/comments/3eo2cx/why_did_roman_lorica_segmentata_armour_not/
https://www.reddit.com/r/AskHistorians/comments/1dx0v2/why_did_the_roman_army_choose_to_abandon_its/