Leaving the "free" part aside for a moment, since this sometimes gets confusing for people and may go in different directions on licensing, why have more proprietary software companies started open sourcing their efforts in the last several years? Is it purely a marketing tactic alone? Isn't there a lot of benefit they derive from giving something to the community and also having the community participate and accelerate the development a lot more than they themselves could do it? Of course, not all projects are the same, and community interest and involvement would wary. But on average, if there is no advantage except for marketing, I doubt for-profit companies even wanting to do it (the process of open sourcing itself adds some overheads, plus the overheads of getting feedback, coordinating and maintaining it - it's almost like expanding a team of 10 people to a team of a hundred).
> But at some point in the food chain, software developers need to put food on the table and send their kids to school. How does that happen if all software is free?
Support, sponsorships by proprietary software makers, donations from people who want to make a better world. Not even the technical folks have the time or would want to get the source code for software and maintain it all the time. So some dedicated person would still be working on the maintenance and improvement of the software. Free software doesn't mean one cannot sell it either. It's just that others will also have the same freedom to sell it if they invest the time and money to compile/build/distribute it.
Before anyone asks how a lone developer would find the market, that problem exists even for developers of proprietary software (mobile app stores are great examples of the huge skew in the distribution of total earnings from app sales across developers/companies).