I wouldn’t call it laziness, as they went through the effort to make an entire set of armour customizations for them. Enabling regular transmog would be the easier option.
It definitely appears to be a design choice. They must have either decided that for the new race to have good visual fidelity, it would require custom armour shapes instead of just overlaid textures, OR good body texture fidelity required a new layout that wasn’t compatible with existing armours.
I might take a look on the model viewer sometime to know for sure.