[vec]

No one would go out of their way to, but it's pretty common to have these cases break because no one's ever bothered to test them. On screen keyboards don't have characters no one will ever type, fonts don't have characters no one will ever display, sorting and string manipulations may not bother to handle accented characters correctly if there will never be accented characters, etc.

No one actively thinks "I'm going to intentionally omit solid unicode support"; we just don't bother with it until we feel there's a good reason to, and by then it's often too late.