Because you have no idea what Norwood you're headed for in the future. If you're gonna be a Norwood 3, 4 or 5 you'll probably be okay, but if you're headed for a 6 or a 7 you will have wasted valuable donor hair on a small crown area of your head, and you're gonna look real awkward with just that patch on your crown.
I suppose you could always go for a repair job and transplant those 1,000 grafts to another part of your head again, but why go through all that??
Why not be patient and see how your baldness pattern progresses first, and then make the necessary transplant(s).
For now I'd stick to meds and Toppik as others have suggested.
Also I think most ethical doctors wouldnt touch your head because of unknown future Norwood progress.
Just my $0.02 worth