I would add that people have a good idea what STEEM is worth, and that it is useful on this site, so they don't want to spend it.

Also, once anybody uses a currency for a long time, whether STEEM or USD, we begin to place a value on it. I inherently feel attached to my USD and STEEM because I know what I can use them for, and I have known for a year+ that they have a worth. It's simple psychology, we just don't have that deeply ingrained sense of value for Future Tokens because we haven't valued them for very long. It's a gut reaction. Using some token/point instead of actual money is an old psychological trick in gaming designed to get people to spend more.