You are right, They are only interested in selling their own tours, which probably makes sence since they are their own company ( not a part of the ship.. as most cruise line destination services are).
But.. they do book for you private cars and tours for your own group.. so you do not have to hassle in advance ( a very nice thing) when you get on ship go to destinations and they can help you set up drivers for yourself ( or your group).. this is great in countries where many of us die hard travelers can not assist you with drivers or guides, and the ship then, will become responsible for you to get back to the ship before they cast off..