Rebuilds in the NFL are tricky. The league has a number of means of enforcing parity, but while the draft system is a huge advantage to a struggling team, the salary cap means that a team locked into bad contracts might need years to reset. Every so often, though, ownership tears off the bandage, fires a GM, and tries to get back into the mix of relevant teams.
Not every team actually needs to be “rebuilt”, even if there is a change at general manager, however. As a case in point, when Brian Gutekunst took over as the GM of the Green Bay Packers, the team had won 17 of their last 32 games (with a playoff run only two seasons before), had a future Hall of Famer at quarterback, and had a number of solid players in place.