Interestingly, even though he's a Hornet & "Rhino" driver as well... he elected (or was "voluntold") to go up as a Mission Specialist rather than a pilot astronaut.
Maybe he wanted to be a spacewalker rather than fly the orbiter? or get in on a shuttle flight before it gets shut down rather than not at all?...
NASA may have made the decision to not train him as a Shuttle pilot since they would probably only get one flight out of him before they retire the shuttle. Given the amount of time and resources they put into training a Shuttle pilot they probably thought it was not worth it.
P.S. He still looks like a Q.......