Not everyone can. Here in the US, doing so without family support / fallback if you fail out makes it extremely risky. If you're supporting yourself completely, having to work gets in the way of going to school (immersion while working full-time, especially at workplaces that demand all your time is basically impossible.) Others succeed in a work setting, but struggle in school. Still others don't want to deal with mounds of debt, and have no college fund/trust fund/aren't good enough to get scholarships. There are lots of reasons.
The more I learn about the US educational system, the more I consider it sucking majorly. I don't know how you can put up with that stuff. I already consider it a source of major social injustice, that here in GER you will only receive state-help for the first 5 years of your studies. But it's at least still possible for everyone who wants to get a degree, if they are willing to exit with something like 10K€ of interest-free debt, payable over 8 years (and have something like a 10h/week job on the side, which is incredibly easy to get as a CS-major).
I guess I'm just overly priviledged by the german educational system… :-/
https://medium.com/@opirmusic/why-software-developers-should...