The PR type approach comes from the Linux kernel where there is essentially a hierarchy of gatekeepers with increasing trust and responsibility. It is a very individualistic type approach (i.e. if you merged it into your branch, it's on you and speed is a non-goal for the most part). This is often different from many software projects as it is like a collective where often, no one really has individual responsibility for anything (it is more like collective responsibility), speed is everything and there are certainly no gate keepers - maybe the review actually doesn't matter that much in this context.