Legion brought the artifact system, where you are locked to one single weapon at each of your roles/specs.
Playing a dps warrior with shield would be impossible in this system, because you would use 1 weapon for 2 roles. It would be unnecessary for a prot warrior to invest time into an other weapon, just to have an offspec dps role.
I want Gladiator's Resolve back as a talent once we get rid of this artifact weapon system, because I (and many other warriors) just need a mid-tier (aka decent) dps offspec for non-tanking situations.