Well written GitHub issues and PRs that you can reference in your git commit also don't save you from commenting code. I mean please do not reference an issue in a code comments, but describing to other people what a function in general does goes a long way to build understanding.

For new contributors it's probably also more useful to see the latest snapshot of the code base and code comments than having to check a git log in order to find out why a function would be written in the way it is.