My answer would hearken back to one of my earlier answers and that is the fundamental difference between the negotiation of provisions and obligations that form a treaty and the enforcement of an action that is perceived to violate an international trade obligation.
It's not surprising that the pursuit in the WTO was done on a totally separate track. The pursuit by Canada of allegations that the EU was not abiding by its international trade commitments is an entirely separate issue from the negotiation of such commitments and of a new and stand-alone treaty.