Western music has certain "rules" that our ears are used to. If the computer limits variation/random-ness to stay within those rules, it will sound at least "pleasant", as the bot won't let you drive outside the lines. However, the real artistry is knowing when and where to break the rules. A tune that sticks to all the rules risks sounding stale or ordinary. You gotta know where to spice and spike it to move to the next level.