If developers had spent a little more time studying sociology, history and government; they could recognize this problem with open source as being common to virtually ALL communal social systems.
The problem --- freeloaders --- aka human nature.
Communal systems typically lack incentive. People benefit whether they contribute or not. Over time, more and more people become content to allow the real zealots carry the load.
This has all been done before and no one has ever managed to sustain such a system over time. A last ditch effort to avoid collapse is often forced labor (aka slavery) --- which some are now proposing for open source.
All totally predictable and somewhat humorous --- but mostly just sad.