Did you know that many (most?) key open source contributors are employed by companies specifically to keep working on their open source projects? This is true of kernel developers, language maintainers, and many more.
Open source contributors are typically privileged white men who can afford to work for free and give away their work because they can and they enjoy showing off.
This puts people from poor backgrounds who can't afford to spend days on projects for free as they have bills to pay and mouths to feed at severe disadvantage. Why companies would hire developers if these cool kids give everything away for free? This is much bigger problem than you think.
So you presume that there is a fixed amount of development work to be done at companies and by using open source software for free they are hiring less people?