You're missing the point here. Willis, Pippen, etc.. nba players grind out an 82 game nba season and a retired vet wants to jump in on a team that's already good, and thus take an enormous shortcut to reach the goal of a championship. Why doesn't Jordan just un-retire and join the Bulls for the playoffs?
I always figured Willis wasn't on a team because no team wanted him at 44. It's not like Kevin Willis wouldn't have played an entire season imo.