An American-made airplane instead of a Brazilian-made one? But I suspect that's not the main reason (but it still is one). Fixed conventional gear vs. retractable tricycle gear may be a factor, as there likely will be a lot fewer maintenance issues in a remote airstrip.
I am deeply skeptical of the Air Froce getting behind a fixed-gear prop-driven air strike aircraft. That need has been around since the Spad was retired and there have been proposals for such aircraft dating back to when the Spads were still flying. So now, something like over fifty years since the guys on the ground have been asking for such an airplane, the Zoomies are going to buy one?
They've been in love with swept-wing jets for a very long time, witness the multi-decade effort to bury the A-10. I submit that the only reason that the Air Force is supporting this project is because the alternative is using armed drones. If there's anything they hate more than straight-wing airplanes, let alone props, is drones.
(For good reason, I might add. Nobody goes through military pilot training to wind up flying a glorified flight-simulator.)