A ledger of hashes doesn't prevent someone from publishing a new version of a package with the stolen credentials. What you advocate in this thread is setting

A ledger of hashes doesn't prevent someone from publishing a new version of a package with the stolen credentials. What you advocate in this thread is setting aside defense in depth. Could the attacker have used the stolen credentials to pivot to other machines and ultimately gain access to the GPG keys? Maybe, but it's a hurdle, and not a small one. The more hurdles we can place in the way, the less likely it is that small mistakes cascade into total system failure. There may be legitimate reasons to not to use package signing, but this is definitely not one of them.