They basically have to weigh up differences between...
1. PvP and PvE gear, and
2. Undergeared lvl 50's and PvP geared lvl 50's
If they close the gap between freshly levelled, undergeared lvl 50's and the PvP geared lvl 50's (which is only sensibly achieved by nerfing PvP gear), then they will reduce the effectiveness of PvP gear in comparison to PvE gear (which is what most PvPers are complaining about).
Conversely, if they close the gap between PvP and PvE gear (by buffing PvP gear), then they increase the gap between freshly levelled, undergeared lvl 50's and the PvP geared lvl 50's.
The most complete solution to this would be to nerf high-end PvP gear (to close the gap) AND nerf PvE gear by even more (so that PvP gear is more effective in PvP then PvE gear). This means they would have to change the difficulties of every PvE encounter, which is unreasonable to expect.
Tl;dr: You can't have your cake and eat it.