I think it's as simple as them not doing the math. Self employment taxes, gas, vehicle wear, etc. They just see the check is bigger than what their prior minimum wage job was. Probably true for Uber, Lyft, etc, also.

And, to be fair, it's more flexible, as you say. I suspect some drag their kids along, or work for Instacart after their day job (or other obligations) is done, etc.