The recommended setting for ai difficulty is AI7, yet last time I installed it defaulted to AI1.
The reason the defaults are set to something "easy" rather then the recommended is that first time players aren't going to read the details of how things should work, they're going to go into the game and get confused, and get crushed, and think "this game sucks".
Which is pretty much the opposite of how you advertise things with good word of mouth.
If the player goes in and plays things on the "defaults" and finds the game really easy ("yay, I'm smarter then the AI, I won!"), they're then going to replay it on a harder difficulty level if they enjoyed the game. At which point they'll probably actually read the tooltips and alter things accordingly.