It’s not just the duration of the visa. In order to work as a CFI people needed the OPT (OTP?!) option that graduates could get right upon finishing whatever degree/license they obtained. And I think that this option is under fire from the Trump administration because it basically got a lot of foreigners a foot in the door to get employer-sponsored for a real work visa aka „stealing jobs“. I don’t know how much this affects flight schools though. You are surely allowed to come over and spend Dads remortgage on a US flight school business, but work...?