Looking at all their back selections, I always had the impression that they never really took the time to know what was going on in the board game industry. Some are so silly and happened in years with such clever games I can only assume they were completely unaware of what was going on.
Sorry to reply to an older comment, but I just stumbled on this.
Understanding how the Mensa Select award is given my help explain what you're seeing. The only games that CAN win are those that are submitted to the competition by their publishers. Many clever games are not submitted, and thus do not win.
The Mensa Select judges love to play games and are very aware of what other games are out there. The fact that Dominion, Suburbia, and Euphoria have won recently shows that even "hard-core gamer" games can win this award if their publishers make them eligible.