Here is my thought, the gig economy is so effective because smartphones makes humans more productive in general. The phone is a great force multiplier, especially in a service based economy. Adam Smith introduced the concept of division of labor, what's more specialized than being an on demand driver?
The problem is that the cost of buisness (car ownership, etc.) is not factored into wages, and that labor is weak, so workers are being exploited.
When productivity is this great human labor becomes more like a commodity.