I got in this same discussion with gregkh on Reddit, and Torvalds in person. Linux development is much slower than many large software engineering firms, because the gatekeeper model has many more integrators and reviewers as a proportion of the members than the "pull request"/ team code review model

Acceptance is certainly part of it, but 8 changes per hour is 8-10 email threads per hour, which is just not that hard to track as an individual, thus no need to change anything. Right now at work on a large (200ish) team, I get cc'd on about the same amount of patches.