I agree I don't like rookies, for several reasons.
First is what all3 said, which is it's a random draw who you get or how good they are. There is no skill involved, and you don't get any input at all.
Second, it allows for changes in strategy based on usage of the rookies. For example, a strategy used by many (and myself at times) is to only draft players for so many minutes and expect rookies to play the rest. That ends if rookies end, and you have to get enough minutes or forced to deal with fatigue.