Even the most clueless and innumerate person is going to notice when they've been working and getting paid for a month, haven't paid any bills yet or bought anything but food and gas, and still have $0.
The problem is that gas is a small part of the equation. You also need to account for depreciation, increased repairs, and opportunity costs (e.g. Uber may require a newer car than you'd otherwise get). It may look like you're making money because you make more than you pay in gas, but I'm guessing people aren't noticing that their day job is subsidizing their side hustle for infrequent expenses.
I use the IRS figure of ~$0.50/mile to ball park an opportunity. When I calculated it for my car, I got closer to $0.25/mile, but that's because I got a good deal on a reliable, used, efficient car (~$10k for a 60k mile Prius) and I do most of my own maintenance. The average driver (having a shop do repairs, worse mileage, buy from dealer with loan) will likely be closer to the IRS figure.
