Why specifically social media? It's a function of communication efficiency. It's why church is associated with this sort of cattiness, everyone knows everyone and is brought together regularly to provide a venue to trade gossip. It also supplies the moral standard by which everyone is evaluated and one's social status is tied to how well one appears to meet this standard. The cattiness is just status games playing out given these constraints.
Why 2010? It's when the "always online" culture went from niche nerd to ubiquitous.