It is not just that everyone knows how passwords work. It is also that you can always enter a password. What if I don't have my phone to scan a qr-code? What if I want to use a minimalistic browser that doesn't implement a key pair store and I don't want to or can't set up one external? What if my minimal browser is text only? What if I'm on another device and don't have my stuff on there? I will pretty much always b…
Yubikeys are not difficult either. You enter your username, you focus the password field and you press the button. There, you're done. If anything it's easier and more convenient than a password.
Passwords are just the lowest common denominator. Everybody can memorize a character string, not everybody has a smartphone or yubikey with them at all times.