Status and control are a currency too.

I worked on open source because I enjoyed the work and because it had control over the final result. Other people did it because of status it gave them in the community. There's plenty of people willing to work on something for "free" (no money) as long as they are compensated in other dimensions such as ownership, status, control or simply enjoyment.

UBI could help here too, since those people still need to eat. Or, society could admit how dependent it is on open source work and pay maintainers and contributors from taxes.

The issue is obviously that most people don't even know what open source is so it's not an interesting political debate topic.