Hackers need just one chain of tired persons to breach a system. Sometimes length(chain) = 1, that's when bad things happen.
Anecdotal PS: I used to work at a bank and had to rotate my password monthly (sometimes even more, because there were unfederated systems that required another password, also with rotation). Eventually all my passwords became [short STRING] + [autoincremental INT]. We had MFA, so it didn't matter that much, but that makes it even more hilarious.
Paper can't be hacked, and writing down the password allows for more complicated passwords. In case someone gets access to your wallet, you still keep a portion of the password not written down.
(And if someone gets physical access to your stuff, you are hosed in general, because they can just install a keylogger. So even keeping your password fragment on a post-it under your keyboard would be fine-ish.)
You probably should know that recent smartphones (the most likely devices to ask for a wifi password at home) have features to share a password right in the settings. iPhones will simply ask you (or anyone connected) to allow them, and androids have some sort of sharing enabled (via qr code generally).
It’s especially annoying when a company enforces these brain dead policies on employees. You want people to waste mental effort changing their passwords by 1 letter every 3 months, just to appease some IT manager? Give me a break lol.
I’d rather have a long complex password that i remember and remember ONCE.