The way that I understand the situation is:
- the PEP contains all the information like “Why did we do <thing-we-settled-on> and not <different-thing>”
- the PR to packaging.python.org adds a page that describes <thing-we-settled-on>
Whether you want to describe <thing-we-settled-on> in the PEP’s text, is the part where I’m not 100% clear so I’m gonna say it’s whatever the PEP’s authors want to do. 