I'm not saying it doesn't suck for this person, but product market fit is a thing for open source too. If people need it they'll use it and contribute until something better comes along. If not, your idea wasn't the one. That doesn't mean it's not possible. Nearly my whole life runs on open source software, so it's pretty clearly sustainable.

over the years, using "open source" has become an excuse to avoid paying for software

Um. Yes. And to be blunt: obviously. And in return, I give away software I create for free whether people need it or not, and try to give back in the form of contributions too. But I've never once given up my day job for it. Would that be nice? Maybe. But open source software is more frequently sustained by passionate people using and expanding it for their own projects and not by expecting people to pay you for your efforts when you're likely not paying (nodejs, github, ahem) for the software you're building it on anyway.