That's a legit good question. I'm not arguing it should be done, just that it wouldn't be the end of the world. The point is, there are many incentives to vote, aside from the curation rewards. The whales have a significant stake invested, and the real way to get a good return on that is for the value of Steem to go up. So if they vote to improve the user experience, speed up adoption, make users happier about the 'fairness' of author rewards distribution, that has a real potential to increase the value of their account. A kind of indirect financial incentive to vote wisely. That's not to say there aren't benefits to the current curation system.