You already get tomestones for playing PvP. Adding lvl80 gear for wolfmarks would just mean you double the pool of gear upgrades, or even unlimit it, cause wolfmarks have no weekly limit. It would be imbalanced, if it wouldn't be something like i430 gear atm.

The big issue is the entry level for PvP, it is level 30 - if you add level 80 rewards, all the people can't even use them. That is why stormblood gear is level 1.