Mostly because it's just a standardized AI and the races don't have individual personalities yet, they all share common preferences. As to why, what do the minus and plus columns tell you?
As an example, i'd like to see the iridium corporation give extra ++ relationship bonuses for trading, and a penalty for not trading with them (if you have the tech and several trade routes). I'd like to see the dregin more warlike, and have a desire to expand borders constantly.