"Everyone focuses" = nothing gets done. I've been at places like that, where a post-mortem happens, a course of action is decided on...and then no one owns actually carrying out that course of action.
You could argue that "It should be assigned" - yeah, it should. But assigning it implies either "here is the team that is responsible for it", i.e., this is the team responsible and they need to be told to fix their shit (which very much sounds like blame), OR it implies "here is the team that I am entrusting to fix it DESPITE their obviously not being responsible for it", which is just as bad, since it implies that the team that 'is' responsible for it is incompetent.
The only healthy option is that the 'responsible' team stands up to say "hey, that's ours; we'll fix it", and the only way they'll do that is if you have a culture of safety and ownership.
Also, one thing to make clear - ownership = responsible = blame. They're all words for the same thing, just different implications. You can't have someone 'own' something without making them responsible, and apt to be blamed if you don't ensure the culture is one that does not attach blame. That's really what I was getting at; of course you shouldn't blame. But, you can't also avoid ownership. But ownership implies you know WHO to blame, and so blame comes very easily. And it's very easy to mistake pointing out responsibility/ownership for something as blame; I have had multiple managers tell me "it's not us vs them" when I've raised up the fact that I'm unable to deliver to deadlines because I have been unable to get anything from product.