In the case of Yahoo's login form, the username is explicitly not echoed because people often have quite similar usernames, so they will try to login three times with the wrong username (it exists, it's just not their username) and then open a support ticket, etc.
(It's Yahoo. This is the single most-used piece of UI on Yahoo other than the front page. Do you really think we don't do it because we're lazy? We never got around to persisting the username in 14 years of endlessly recoding the login page?)
Comments
In the case of Yahoo's login form, the username is explicitly not echoed because people often have quite similar usernames, so they will try to login three times with the wrong username (it exists, it's just not their username) and then open a support ticket, etc.
(It's Yahoo. This is the single most-used piece of UI on Yahoo other than the front page. Do you really think we don't do it because we're lazy? We never got around to persisting the username in 14 years of endlessly recoding the login page?)