Zappe wasn't in demand at all, media spin.
He was so in demand 31 teams refused to sign him to their roster and a few offered him a spot on their practice squad, that's about as far away from demand as you can possibly be.
That's on the verge of being out of the league, also Bill didn't "know what he was doing" he just didn't care if he was claimed or not.
You don't expose anyone you think is valuable to the entire league, he basically said Zappe sucks and the whole league knows it so if no one signs him then we'll stick him on the practice squad and hope to get a better backup and if we can't get one as a last resort we might have to make Zappe the backup again.