We do sign our packages, but the threat model is to minimize the time it takes for users to not have to trust us.

It is critical to encourage many independent verifications that it be as fast as possible that someone can go from a clone of our tree of pure source code to the exact release hashes we publish.

Adding any binaries to that means someone that distrusts us must now go build those past releases as well, and if they rely on binaries, they must build those past past releases as well. This approach would make verification time go up dramatically every release.