1) prone to typo error, especially as the password is generally hidden
2) number & capitals are a pain on mobile devices
3) ever harder to remember (ie. where the @!#$ did I put the capital)
Because it has fallen into quasi-oblivion. If it was that much of a perfect society, it would still rules over Mediterranean coast, Latin would not be a dead language.
Moreover, if current society is so much like the Ancient Rome, we have to worry, because the next age, namely the Middle Age, has been a long period of general regression.