Now we know why.
Willis, the team's inside linebacker and leading tackler, wanted one more chance to play with his teammates before the season ends. He knows some of them won't be back.
How many is unknown, but with a new general manager and new head coach still to be determined, Willis understands that changes are coming.
"As bad as I want to go out there and play, just my will and desire to compete and give my teammates and this organization everything I have, it hurts not to be able to complete this season," he said Thursday. "Even though we're not going to the playoffs, it's the pride aspect of it and being able to play with these guys.
"Truth of the matter, some of us may not be here next year. So I wanted to go out there and at least play with them."
Among the 49ers players on defense who become free agents after the season are linebackers Takeo Spikes and Manny Lawson, nose tackle Aubrayo Franklin and safety Dashon Goldson. Cornerback Nate Clements is due to make $7.25 million and isn't expected to return.
"We haven't sat down one and one and talked about it," said Willis, who has started all 63 games of his NFL career, "but we've kind of mentioned it as a defense. A few weeks ago, we (talked) about the opportunity that lies ahead of us as far as just wanting to be where we wanted to be. That's a high possibility. That's a fact that some of us won't be together next year."
Willis said a second surgery, which was performed by team orthopedic surgeon Tim McAdams, was needed when an X-ray showed that the broken third metacarpal bone in his right hand had shifted.
Willis said three pins were inserted. The estimated recovery time is 6-8 weeks, making him uncertain to play in the Pro Bowl on Jan. 30.
BOWMAN'S CHANCE: Although rookie NaVorro Bowman has subbed occasionally this season for Spikes at the Ted linebacker spot, he'll be moved to Willis' Mike position Sunday.
Defensive coordinator Greg Manusky, however, said he stressed to Bowman to study both positions this season after Scott McKillop was injured in training camp.
"With young guys, that's the concern going in, just to study that position more than anything," Manusky said. "Once the season progressed and Scotty McKillop kind of got banged up and got hurt, I went to Bow and said, ‘You've got to make sure you know both. You've just got to pay attention.'
"With most linebackers, you want them to understand both of them, but it is a little bit of a different position for both guys. He took the challenge and he understands it. I think he'll be fine with it."
SAVE YOUR MONEY: Spikes, the team's player representative, said he's been telling teammates to save their money in case of a lockout. For most, despite their big salaries, it means moving to cheaper locales.
"As much as we all like the mild weather here, at this point you have to do what makes sense, and what makes sense is controlling your budget," Spikes said. "We all know it's not cheap to live here. With the sunshine comes a nice hefty penny with it.
"A lot of guys are not in the position that I'm in. I'm blessed. I saved my money and played for a long time to where I know I'll be OK, but a lot of guys will not because of their draft status, (or they) came in as free agents. So with those guys, if you have to get a job with all of the connections you made, even in college, do what you have to do to support your family. That's the bottom line. That's what it's going to boil down to."