Most likely reason is that there is no clear return on investment for throwing resources at building a colony on Mars - so what politician is going to choose to

Most likely reason is that there is no clear return on investment for throwing resources at building a colony on Mars - so what politician is going to choose to spend money to make life possible on Mars when it could be spent (or the taxes not raised) down here? NB I don't think private capital would ever be enough to get a self sufficient colony started.