Enforcing something like this puts a lot of, IMO, undue pressure on the devs and signals that some reviewers are trying to skirt their responsibilities of being

Enforcing something like this puts a lot of, IMO, undue pressure on the devs and signals that some reviewers are trying to skirt their responsibilities of being accountable for the code base. With unreviewed code, you can more easily point fingers at someone else. Even if there's no need for that, when it is time to update the code base again, now only one person is familiar with the code, so others are less likely to take it on.