the biggest problem is that there is no one place where rejected patches are ever together today.
there are many ways patches can be sent, to many different people (and in some cases the patches themselves aren't sent, just a request to pull from a git repository that may disappear in a few days)
it would be a significant amount of work to gather such patches, let alone maintain them.
there are patches like this today, but they get hosted and maintained by the people who care about them.