4 sets times number of races times number of genders...
The base sets take a certain amount of time to make, then they all have to be adjusted to fit each race and gender.
Going unique per role would increase the burden of work by a lot.
Quite simple really.
And that's just one set of gear... We'll get a few more new gearsets in this patch.

I don't know how fast these things can be made while still making them actually look good... (not that looking good matters because there will always be people that bitch about their particular set looking like shit)