I do this, but it's not all roses. Getting and keeping those contracts continually takes effort and time. It's stressful when you don't have much line of sight into the future. And even though you can charge a high hourly rate, it's difficult to work lots of billable hours. I need time for context switching, administrivia, marketing. And the one problem I don't see discussed much: on-demand motivation.

If you work a salary job and don't feel up to it for at the moment, you can coast for half a day and get your shit together. On your own, that's a half a day of lost money. My brain needs breaks, and I just can't do code 40 hours a week and not burn out. I've tried. It just hasn't worked. So that downtime is a requirement, and you lose money for it.

The best part is that a decent programmer can make a moderate income working relatively little. Or you can make a lot of money if you work very hard. It's your choice at any given moment. But don't underestimate the drain of having to work for one to three people at a time, managing your time, and making sure the pipeline doesn't run dry all at the same time. It's pretty annoying/stressful when two important clients have deadlines on the same day. It's not like you can just pull in more help. Or if you can, you then have two problems - you have to go out and find the help, manage it, etc.

I don't think I could bill more than 25 hours a week and keep my sanity. But I'm not exactly a workaholic, and 25 hours a week is a pretty good living.

Milage may vary.