I believe it's to do with the lease on the aircraft. As we don't officially own the aircraft outright we can't put them into TLZ's or attempt Tac sorties in any way shape or form.
If it makes you feel any better the Spams put one of their C17's into Bastion many many months ago.
I can't wait till they can go direct. Taking a little pressure off the massively overstretched J fleet won't be a bad thing!
