The schedule in which National Football League front office operate is different than what both players and coaches run on. Instead of having their hiring and firing cycle mostly occur at the end of the regular season, those decisions are often made after the NFL Draft.
Yes, some general managers are let gu after the regular season, but it makes things more difficult for the NFL Draft being just three months later. That is how the New England Patriots handled their business, as they named Eliot Wolf acting general manager instead of looking for a permanent solution.