How did we as an industry go from "Passwords in notebooks are insecure, use a password manager" full circle back to "Password managers are insecure, write your passwords in notebooks"?

There has always been more nuance. The notebook is basically air gapped, but since using it is painful, most will rely on shorter, simpler, passwords and reuse them. That practice is highly insecure and was even more problematic in the days before widespread 2FA on the more crucial online services. As a teen I could have had for instance blizzard get breached and collaterally lose all of my csgo skins.