Why do festival-winning films fare so middlingly at the boxoffice?

Shawn Levy, writing for OregonLive.com:

In fact, it turns out that few films that win even the most prestigious prizes at the most prestigious film festivals ever become true box office sensations.  Consider these Sundance-winning titles:  “Like Crazy” (2011), “Frozen River” (2008), “Sangre de Mi Sangre” (aka “Padre Nuestro”) (2007), “Quinceañera” (2006), “Forty Shades of Blue” (2005), “Primer” (2004), “American Splendor” (2003), and “Personal Velocity” (2002).  It’s an estimable list, with some real treats and a couple of Oscar nominations in the bunch.  But the eight films made a total of $14,980,000 -- combined.  Boxoffice success is surely not a sign of quality, but it seems that films that get such a huge boost from America’s premiere festival ought to do better, no?

I am shocked, shocked to discover that festival programmers and audiences don't represent the general moviegoing public.