You seem to imagine that all those contributors were once unemployed. That was never the case.
The typical open source developer has always been either (1) gainfully employed at a programming day job, (2) employed to actually build FOSS, or (3) in academia.
There's at least as much open source development going on now as ever before. It's just that the attention has shifted away from desktop apps.
I contribute to GNOME, and that is not "working for free". It means having a fun hobby. If I'd get money for it, it would no longer be a hobby, but work. I did hear some people say that their hobby is the same as their work. IMO, work is more restricted (try doing nothing at all for 3 months with your hobby, then repeat for your work).
The typical open source developer has always been either (1) gainfully employed at a programming day job, (2) employed to actually build FOSS, or (3) in academia.
There's at least as much open source development going on now as ever before. It's just that the attention has shifted away from desktop apps.