The beauty of this proposal is that it isn't a new standard -- it's suggesting that we use the already existing words and stop using the less understood acronyms.
authn/z are more abbreviations than acronyms, which come with less organization or domain specific required knowledge, which is the typical complaint of acronyms
They aren't universal because folks like the article author keep trying to make fetch happen. Authentication, Authorization, and Accounting (AAA) are bedrock security concepts. They sound fine out loud, and I have no idea why a verb form would be a requirement for an abbreviation.