I discovered the answer to this question a while ago when working in an uber eats competitor. Drivers continue to drive for uber long term because they literally cannot do much else.

Take toronto, ontario for instance. I've spoken to hundreds, and recruited hundreds of drivers, and ~85% of them speak very little english, have extremely few skills, and are in a position where they have to pay bills NOW, and can't afford to invest in themselves. Its sad, but they're trapped in a vicious cycle.