How can that be anywhere near financially sustainable.

All you have to do is basic math.

Monthly car payment (which is higher if you're poor) + monthly gas spent (which is higher if you buy it in a poor neighborhood) + monthly insurance (which is likely to be higher if you're poor, and/or live in a poor neighborhood) + maintenance is very often far less than what it costs to take a rideshare ride 14 times a week.

When I drove for Uber, about 20% of my rides were people commuting to and from work who could not afford a car.