They are not instrumental in making breakthroughs and to innovate.  You need creativity, the ability to see the big picture, and think outside of the box.

Most engineers, scientists and software developers reach their shelf life in the late 30s because they can't transition beyond just following complex instructions. Most technicial field people get laid off becuse they are at the height of their slalary scale but the value is not there.

If these people are so creative and able to think out of the box, they would not have been street vendors.  They would have doing other exciting stuff.  Even start-ups.