My mother signs out of her email every time she closes it, and does the same for other websites as well. She's the only one who uses her computer, and it has a password on it (mostly because Windows won't do file sharing without one). She still refuses to stay signed in.

Not everyone wants to stay logged in, and not everyone uses a single browser; I occasionally use the wrong browser profile for something because I cbf loading up the correct one; in these cases I usually load the website in a private browsing tab to avoid container/addon settings interfering. When I can't log in easily, I get quite annoyed.