Warglaives are iconic to DH, yes.
But these specific glaives are iconic to other classes. The first thing that pops into my head when I think about them is a rogue. In-game it makes sense (historicaly), lore-wise it doesn't.
I'm not 100% sure, but. Is the TW xmog version for DHs slightly different from the original model?
They could leave DHs with that slightly altered model and give the other original classes the old model.