On some devices it may be easier to enter a long password from a restricted character set than to enter a shorter password from a richer set.

For example, I've seen TVs that allow using a numeric keypad on the remote for entering digits in text and password fields, and require use of a clumsy on-screen keyboard for entering letters or punctuation. The on-screen keyboard is navigated with the up/down/left/right/ENTER buttons on the remote, and might have multiple shift states for case and punctuation requiring navigating to and pressing a shift key whenever the password has adjacent characters that need different shift states.

On such a TV, I'd rather enter a 39 character all numeric password than a 22 character alphanumeric password. Entering 39 characters on a hardware numeric keypad is way faster and way less error prone.