>Dave (Content lead): The leg plates are a conscious decision. We tried a few different iterations of the design, and this one read the best. I feel that the old flared armour had given the impression that it articulated midway down the leg.
So that's why!

https://www.warhammer-community.com/en-gb/articles/ma3wgcpx/the-horus-heresy-round-table-crusade-armour-disintegrators-and-more/