The Telegram had a story about the lack of concerts: here's the story.

The center field door is only 12' high, which is a foot shorter than what's needed to fit a truck through, so any touring group is going to have to unload all of their stuff outside of the wall and carry it through or lift it over with a crane like they do at Fenway (which is obviously not going to make sense cost- or effort-wise for any artist that would be considering playing in the stadium).