Probably because SMAA doesn't work all that well with the shader models used on consoles, although Crytek has it in for Crysis 3. It took FXAA a long time to catch on for native support so hopefully SMAA becomes a standard soon, at least for next gen. So much better than FXAA and it would be a great solution for consoles.
Next gen will not need custom AA, I guess. All those solutions are borned just to save resources in the current generation, imho.