Explain why I can't use my PvP Rewards?

[Stormrider]

and in which way exactly are they better?

If you are a crazy min maxer you can get the odd +1 crit or +1 det out of the morale ilvl sync. It is literally plus 1. But some of the gear has acc on it now which would have taken away a secondary stat so you can find better pieces without accuracy.