Why would it need to make <i>any</i> money?  Look at roads: they cost huge amounts to build and maintain, yet the vast majority don't bring in any direct revenue whatsoever.<p>Let's turn this statement on its head, and reframe it as a question: why isn't all mass transit free?<p>(Yes, I understand economically why this isn't the case, and I still think it's a worthwhile viewpoint/question to ask.)