If a person has enough experience at contracting to lean on that reliably, or enough skill to earn ~$80k-$100k per year (to build enough savings quickly for a good runway), then it's definitely not the ideal route to pull a part-time $15/hr type job (it'd be a waste of time).
And it only works well for younger people without a family, as it'll involve 70-80 hours of work per week (at least in the beginning).
It's a poor(er) person's scenario. It's what I might do if I were 19-21 years old again. Back then, circa 1999-2001, I did a lot of web development contracting to fund building things I wanted to build with the rest of my time. It was a quite unreliable path though, as some months were flush and others were bleak. Poor people in that scenario usually don't have degrees from nice universities, they often can't easily get good engineering jobs early on. And if they have an aversion to working for other people/companies, as I always have, then that complicates the context further (CVS & Co are mostly drone jobs; POS, scan bar codes, greet customers, bag items, stock shelves, repeat; and it might help reduce development burnout, as it gets you away from code and out of the house). If you're young'ish, poor'ish and without a ton of experience, it provides a highly workable avenue to go after building a thing you want to build, self-funded, while cutting out the need for early outside capital (the need to give up a piece of your soul to the sharks).