Some want 5 letters, some want a minimum of 10, some want a maximum of 8, some want a number, some want a mix of capital and lower case letters, some want an underscore, some want a special character @#$%@#@%@#%...others don't allow special characters etc.
Obviously there is absolutely no need for something that restrictive. All it does, is that people are stuck using uncommon passwords...which in turn means that they end up writing them down or constantly forgetting them, which bypasses the security.
So how about we create a common set of password standards...one that doesn't force the user to deviate from their common passwords, yet one that does the bare minimum to make brute forcing it with bots complicated.