The reason? There was no obvious replacement on the roster.
But this offseason is different because the 2015 season provided a natural period of transition. Lynch missed nine regular-season games, and Thomas Rawls broke out. He led the NFL in yards per carry (5.65) and average yards after contact (2.68). Rawls is one of five backs since the merger to run for at least 800 yards and average at least 5.5 YPC as a rookie.
Pete Carroll stresses competition, and publicly he will probably say that all the backs on the roster are going to battle it out for touches. But Rawls showed all the traits the Seahawks want from a young back: smarts, vision, toughness and explosiveness. The only question right now is how well he can rehab from the ankle injury he suffered in Week 14. If Rawls can get close to full strength (and that is the expectation), he should be the starter going into next season.
Of course, the Seahawks would like to give themselves as many options as possible in the event that Rawls suffers a setback or another injury. They generally rotate in a second ball-carrier anyway.
Michael returned to the team late in the season and is a restricted free agent. He carried 39 times for 192 yards (4.92 YPC) in three regular-season games. Carroll said at the end of the season that he would like the Seahawks to bring Michael back.
Fred Jackson turns 35 this month and is an unrestricted free agent. He served his role as a third-down back -- pass protecting and catching 32 balls for 257 yards. But the Seahawks might look for a younger option who presents more of a threat as a ball-carrier. That could mean a veteran free agent or a rookie.
It would be a surprise if they took a running back before the third day of the draft. More likely is that they bring in undrafted guys they like. That's how they ended up with Rawls last offseason.
Moves will be made, but the situation at running back without Lynch is not dire. Rawls will take the lead, just as he did for seven games in 2015, and the Seahawks will fill in complementary pieces from there.