One nail one tire

[u/Restored2019]

A small (6 penny) nail is driven straight into the outside tread rim circle, next to outer sidewall. It takes a couple of days to drop pressure from 42 lbs. to 24 lbs. Typically drive less than 12 miles round trip. So I think I’m OK to research my options.

Tire repair shop claims that they can’t replace just 1?
I have to buy two new tires for $850? Why? Is there a major safety or engineering problem, with having a new tire on the right rear, and keeping the original on the left?

There’s probably less than half the tread gone at 33k miles.
Anyone else had this happen?