You can be compensated by "gorging" on other open-source that you haven't contributed to, working outside OSS, or asking for funding to keep working or work more. But if you work privately, you're competing against someone who will work publicly, while limiting someone else who would like to use your private work but can't afford it (like you can't afford others).
You never hear about them but there are also invitation only communities where contributing is required. The benefits are not shared outside.
Any ideology built on this premise is doomed to failure. Successful movements are ones that align the particular interests of individuals with the broader goals of the community.
Dogmas that set individual interest and public interest at odds with each other will always debilitate the effectiveness of the entire movement, and subject it to never-ending internal conflict.
The free software/open source ecosystem has successfully demonstrated how public-interest idealism and for-profit commercial pursuits can not just coexist, but actually complement and reinforce each other. Anyone who's arguing for one side of the ecosystem in opposition to the other is asking for the entire thing to collapse.
However on the other hand, it has been drilled into your head repeatedly that wanting compensation for work is "bad" and antithetical to social movements. You work for the whole, not for yourself. Besides, you (along with everyone else) gets to enjoy the fruits of others free work.
But then after dwelling on it, you realize that 90% of the people holding you to this ideology aren't contributing much if anything at all, and just gorging themselves on the work of a few.
So now you either consolidate power into your hands (nazi mods), lose motivation (project decays), or become an "evil" capitalist(start charging money for access).