Promoting by promising to fulfill a particular obligation creates the obligation. I'm not sure "showing that you care" is specific enough.
In any case, you are shifting your ground. Before you said that just making the software available and having enough people use it creates an obligation. Now you are saying that "promoting" it does. When "promoting" is properly unpacked, you will end up agreeing with my position: either the software author has made an explicit promise to provide support, or they haven't. If they have, they have an obligation; if not, they don't.