$2B is still nothing to sneeze at, but it's less than Microsoft paid for Minecraft.
YouTube could probably outsource it internationally, but that'd just spark a new round of outrage: "Why are global community standards set by an American technology company outsourced to poor workers in the Philippines? Are these the people we want deciding our values?"
One is an investment/one time purchase and the other is a long-term annual liability, slated to grow.