Here is the dirty secret, and it applies to all of the tech sector, not just games.
Interviewing for talent is hard. Getting an idea of skills in the course of a day of interviews is *hard*.
Even looking at past performance (especially in games) is hard. Are they ready for the next project, or did that last game burn them out?
(Seriously, I have known people who would not hire people out of studios known for high crunch, because they had had too many cases of hiring people who were burned out. You had to go somewhere else first and prove you were ok, before they would consider you)
Whiteboarding questions aren't there to prove how good a programmer are, they are to weed out the people who can talk all the right talk but are inept.
There are all sorts of schools of thought on how to interview, and there are trainers out there touting methods for companies to use. People keep looking, because this is hard, and because the cost of a bad hire is high.