I thought part of how the USA postal service works is by flying mail on commercial planes. I think it was part of making passenger flights profitable and accessible to the public at some point?

The airliners regularly make more revenue carrying cargo than with passengers on board.

Think of all the deliveries in your town. Some are almost coincidental with your trips! But the hassle of figuring out how to do one or more of them is not worth the effort.

Startup idea: It's like Uber, but for mail!

"Get paid to go on road trips to see and explore the country." or "Planning a vacation? We'll help you pay for it and take you to exciting new places few rarely get to see!" or "Need new pics for Insta? Get paid while looking for backdrops no one else has!"

Please give me my billion dollar seed investment now.

/joke

You didn't mention "AI" so you can at best get 1.5 million.

If the whole point of these flights is training new pilots, would you even want to worry about cargo, especially if it's for a customer?

Well I hope someone with actual aviation knowledge shows up and enlightens us.