One thing that nobody ever wants to see is people scrambling like terrified rabbits as the wolflike specter of blame approaches.
A lot of workplace dysfunction involves blame. We call it the blame game because it isn't really about blame, it's about getting out of doing stuff. If it's not your fault, you don't have to fix it, right?
Collective code ownership can discourage that kind of dysfunction.
The blame game operates on the principle of social proof. If everybody agrees X is to blame, then it's X's fault. Collective code ownership makes tracking mistakes easier, because more people know what the code looks like from the inside. Social proof is still at work, but it's social proof which originates in analysis of the code base, rather than social proof which originates in subjective impressions of clothing style, body language, or tone of voice.
It's important to realize that the blame game's pathetic, whether you win or lose. People who take responsibility and do good work want to be rewarded for that. They don't want to take responsibility, do good work, and then maybe get lucky and win a popularity contest. If keeping good people is a goal in your organization, collective code ownership is one way to achieve that goal.