Board Thread:Lore Discussion/@comment-28142695-20160712153804/@comment-26893431-20160712162635

Might have something to do with the region. The Legions used to conqeur Black Marsh also ditched their heavy rainment and greaves for armor that suits the terrain more than full plate armor. In Skyrim, with all the mountains, it makes sense for them to wear a lot of light armor instead of heavy.