This is the correct assessment. This is not up to the open source community or individual projects to "figure out", any more than its up to me to figure out how not to get spam email.

We’re currently working on a feature that lets admins archive PRs. The goal is to give maintainers more control over how they manage contributions in their repositories. Archived PRs would be visible to admins only, so maintainers still have access to contributor history for auditing purposes and to meet any organizational or compliance requirements. Would this be helpful for you?

What is the benefit of deleting a PR over just closing it? It seems like closing has the benefit of signaling what kinds of PRs aren't acceptable, which deleting would lose.