You see founders parachute straight into consulting or speaking after flaming out of their tech startup. Their team needs to go get jobs.
I can't speak for everywhere on earth but in this current Bay Area tech job market, I can just as easily parachute into a well-paying, full-time gig at $TRENDY_TECH_COMPANY. You build interesting experience & insight being the first-hire and, if you're actually a skilled engineer, shouldn't have a problem finding your next job in about 4 to 6 weeks if things don't work out.
Management consultants make a lot more than code jockeys do.
I'd go off and found a startup tomorrow if I had some way to keep paying my mortgage and feeding three mouths for however many years it took to adequeately replace my current income.
But not everyone is cut out to be a found or has a good idea they can execute on. For those people being an early employee is the best they can do. It's also incredibly more stressful being a founder and a lot of people don't want that. They are happy to take a lower than market salary in exchange for lottery ticket (equity).