Why not? I'd prefer working with OSS for money over proprietary products.
Big companies have an Open Source Program Office (OSPO) where community / OSS skills and licensing knowledge mean you can help the company both consume OSS and contribute back to it.
But still, it's something else to say
"OSS doesn't make money" (which is controversial, if not wrong)
"OSS doesn't make money if you don't have enough time to build the side services and market it because of lack of time meanwhile maintain[ing] a job"
(which most can agree with)