There's a comment in the article that describes it as "land-grab mode". How long did Facebook operate with zero revenue? Twitter? For some businesses, their top priority is to grow the userbase as huge as possible so that when they start trying to generate revenue they have enough users that the tiny numbers they get from each user payout in huge quantities in total.
Would Facebook have taken over social networking if it had been slathered with ads during its growth phase? I don't know. Zuckerberg didn't think so.