I don't know if this is the reason, but going back to the old days of 1st edition, each of the four main character classes had their good stat and weak stat. For example:
Fighters (High Str, Low Int)
Clerics (High Wis, Low Dex)
Thieves (High Dex, Low Wis)
Magic-Users (High Int, Low Str)
If I remember correctly, if you had a Dex of less than six or so, then that character could only be a cleric.