[stubish]

ASCII only is not appropriate in some locales, as the keyboards don't have a-z. This is why in Thailand people tend to use their mobile phone number as their password, because it can be typed on all the common keyboard layouts they will encounter.

Also, with Windows 10 users will often not even choose their username. It gets generated from their given name + surname (which is a whole different issue for people without one or t'other).