If WM works like GB, it's not always in your interest to keep it up 100% of the time. On the other hand, if your BRDs aren't even turning it on, that's pretty terrible.
Also, sight unseen, there's a high probability those BRDs are undergeared like mad, so even if they did use WM they'd still be dead weight. WM isn't so much of a DPS boost that you'd go from 4 to 2 if your weapon is still i90.