The chances of you having a password that already exists are probably much lower than having a username that already exists, amirite?

Not after the recent "Password Mangers" programs/Apps getting hacked, now a bunch of people have those random generated passwords.

Only because so many sites force you to add in semicolons or underscores or something to make your password more "strong".

People who use the same password for multiple things: "Am I a joke to you"