Strength of Pass Words

I recently spent a lot of time and effort to change all my passwords which totaled about 40.  I used the Norton Password generator to create all of my new passwords. After changing them all I went into the statistics portion of the program and found that only approximately 15 of my Norton generated password were considered strong by Norton.  I am not going to change them again but why would Norton generate a pass word that is only considered "moderate".  I would expect all the password from the generator to be considered "strong".  I used the same 8 number criteria on all the requested numbers, which included all possible options to be placed in a number yet some were considered strong some moderate.