I do agree that the tour has something to do with it. But, at the same time I think that this great show has two strikes against it. The first one is that I feel that this is a show that has a limited audience. Secondly, I feel that the location has something to do with it. While it is up on TKTS every day, and while there are billboards that tell you how to get there on the subway, most tourists would rather see a show that is in the theatre district rather than venture on the subway to a part of the city that they don't know to see a show.
Now, I do recall reading something on here that talked about Lincoln Center Theater transferring the play to midtown to make way for a revival of The King and I in the fall. Considering the time, I doubt that that is going to happen. But, I think that if it were, it could help the show to be in a smaller theatre in a more tourist friendly location.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll