It's compromise.
People are lazy and banks do not wish to grant you unnecessary security.
But in apps (or identity card here) you can have PIN longer, like 12 digits, sometimes more.
BTW Do you know that you should never rely on
"Remember Me" functionality of your browser? If you work with sensitive data.
You should keep your passwords aside in some PIN wallet. As is
Keepass and alike. Same (almost same) app for Windows, Linux, Android, iOS.
![:P :P](/forums/images/smilies/p.gif)