When these consoles were being developed 4k was not even on the radar, you can't just add something in that big so near the release dates.
Besides it will take 2-3 years yet for there to be enough 4k content to actually warrant mass adoption (for these things to go mainstream) It could very well take a little longer then that for games to adopt 4k also (mass market that is). We will see this in the next generation of consoles.
Besides have you seen what it takes for a PC to run games at 4k? to do it correctly you need 2 pretty beefy video cards.







