For Heaton, it was a chance to return to his first club and earn a decent wage, but with no expectation of playing games (I think it was 3 appearances in 4 seasons), but he was a lot older than Woodman.
There's been others who have done it. Richard Wright at Man City for 4 seasons without playing a game, Rob Green at Chelsea the same. The clubs don't expect them to ever play a game, but prefer spending more money on an experienced 3rd choice keeper rather than a youngster, just in case of an emergency situation.
I would have thought Woodman at 28 would have more ambition than that, but who knows?