i don't find it to be a baffling question. i think the unspoken part of this is "this is a really stupid system, someone ought to do something about it". i hope in the next 20 years that password managers are a thing of the past, but for good privacy-preserving reasons.
You might as well ask me how many grains there are in my salt shaker.
Interesting academic question, but seeing so many people climb on their soap box is wild.