When you attach any money to it, it becomes tainted with responsibility and emotions. Such as, "should I work on this an extra hour and burn myself out and get those extra 40 bucks for dinner tonight?" That formula doesn't make individuals want to work more on open-source.
Sure they push them towards doing stuff in open-source but that usually almost never leads to creating great pieces of work.
One great and amazing thing that open-source thought us is that individuals can group together and work on amazing things without any economical reward. To me it was always a fascinating experiment outside the usual realms of politics, economics, social-studies.
Nobody would have ever imagined it to work without "money", but it does and it will continue to work. In fact, instead of pushing capitalism mentality inside of open-source we should be doing exactly the opposite: push open-source mentality in other parts of our society.