Because Bethesda is to cheap to have Jeff Baker do Dunmer male voices for a whole game. At least that's what I think and since beth hasn't said anything on the subject I'll continue to think that. Also no one say it's because they're not around ash of Morrowind, because the female voice has pretty much not changed and a lot of the Dunmer are from Morrowind and/or moved from Morrowind to Skyrim/Solstheim.
I'll do you one better:
The whole "canon argument" about the presence of ash affecting the voices of dunmer is flawed. If that were the case, why does Neloth in DB sound just like every other british dunmer, instead of the voice of Baker's Neloth in Morrowind, and Baker's Jiub in Dawnguard?