That’s a false dichotomy, because an ice cream parlor doesn’t stop selling ice cream when they give out free samples, any more than most open source developers quit their jobs (or stop searching for one) to work on their personal projects. Plus, you’re kind of asking the wrong person anyways, because I think I actually do significantly more work for free than I do for what I get paid for, just for those warm fuzzy feelings (exposure being a nice bonus). Plus, I happen to be financially stable enough to probably do this for longer than six months if required even without a full-time job. I basically did this last year when switching jobs (actually around five months, while interviewing around at a leisurely pace) and it was incredibly enjoyable. Felt like I had retired early and could just pursue whatever I wanted to learn or make: if you can afford to do it, I’d strongly suggest giving it a try.
Great, and the if the project you make for a bit more than six months of lots of dedication succeeds people might realize you are an expert in something and try to hire you into a job that is more than full-time and/or doesn't allow other programming with a very nice offer. I would expect you to take that job, but Internet haters will disagree.
Now the project someone chose for its high amount of free unguaranteed support goes off a cliff of no maintainer..
In my experience, I value projects with minimal maintenance over years by a large number of more selfishly invested contributors over the "excited just to be here" projects.