There are a lot of very small companies with less than 10 people in them quietly making good money that have a software system that doesn't need a full time developer. Or, because they can't afford a large team, are willing to hire a few developers part time to reduce the risk of one single person being the sole linchpin for the entire business.
I see a lot of people around here asking "How do I get more clients?" In the course of 8 years of freelancing, I've only had around 10 clients total because most of them have been in an arrangement like this, and they stay for a long time. I've often been the one to end the relationship for it not being a good fit for me, not them running out of money or firing me. They don't come very often, but when they do, they usually stick.
If I had to do the Upwork hustle, I'd have probably quit a long time ago. This seems to not be as true for other professions like design/copywriting/music/etc, but full time salaried development just pays too well to be a freelancer unless you want freedom. Otherwise it's just crappy employment with fewer benefits.
For a good number of years I lived in rural Indiana and worked 10 hours a week for one client at $90/hr and made plenty to live on for just myself. Now I'm working to earn more than that, but with this model it's often a matter of scaling up or down the number of clients you have.
Freelancing gives you the ability to work less than 40 hours a week, which gives you leverage over your time to create the life for yourself that you want. It's stupidly hard to start a SaaS app with a full time job, but freelancing can sustain you on 20 hours a week and then the rest of the time can be spend doing whatever you want (just work less, start a business without stress, travel, etc).