In an interview with Rock Paper Shotgun, CD Projekt revealed the reasoning behind the decision to give the previously beard-less Geralt a beard in The Witcher 3. Michał Platkow-Gilewski of CD Projekt said that they "asked all the girls here, what’s the sexiest thing about the guys in the office? They all said the beards are the sexiest."
Okay the real reason is that "time has passed," but I'm going to keep citing that first quote to anyone who asks. The interview goes into some juicy game bits too, specifically why they chose an open world in such a story-heavy game and how they plan to make it work.
CD Projekt has a lot of hard work ahead of them to live up to everything they promise, though judging from this interview, they seem to be on the right track.
CD Projekt On The Witcher 3′s Open World, Beards [Rock Paper Shotgun]