Most/all of those are individually automated.

Someone checks that they ran successfully, and vouches for it.

Automating the automation can be counter productive.

Like the release process is triggered automatically by a tag, then fails after an hour long sequence of complex steps, which forces you to re-tag, but by then your tag is out there.

Or, simply, it's a bad idea to run the entire process from scratch, but you automated it such that it's easiest, so you fix something about it and the only way to test the release process itself is to release, and you now need half a dozen releases to get it right.