This was also the exact time of all the Google Panda tweaks and the fallout from Google starting to penalize creative commons scrapers of Stack Overflow content. There were a lot of balls in the air and only a few of them were ours, so we wanted to be careful.
When Google is 90% of your traffic, you REALLY REALLY REALLY do not want to get on their bad side, even accidentally, so I can hope you understand why we wanted to be cautious to the extreme here. If Google decides you're not doing things right, it is literally a business ending move.
Unless your VCs and investors are cool with you losing, y'know, ninety percent of your traffic.