The Colorado String Quartet plays new music because it fits the quartet's programming and out of responsibility. Some great music is being written for string quartet now. That's why we're playing it. We shouldn't be a dead ensemble, playing only dead stuff. There's still a lot that composers have to say.
Composers also get a good deal from a quartet.
Unlike a symphony orchestra that has conservative tastes, huge production budgets and rules that can restrict rehearsal time, quartets can throw everything they have at new music. We'll rehearse a piece until it's really good. Composers like writing for a string quartet because they know they're going to get a good performance out of it. Also, we really care about what it is we're doing. I'm not sure an orchestra cares about what its doing.