> she cites an example of people noticing their password manager wasn't autofilling, because it knew they weren't on the expected domain, and then users manually copy/pasting the credentials out of their password manager anyway

One big reason people do that is because probably 99+% of the time their password manager fails to fill the fields is not because it is the wrong site.

It is almost always because the site has done something with its fields that is either preventing the password manager from finding the fields, or is blocking it from filling them (often intentionally).