It's not that Snapchat is critical infrastructure. It's that they've captured the attention of a generation and are going to potentially build things in the future that could define how people interact with technology. I'm not saying that they will, it's too early to tell because they're just getting started. We'll see. But it's much too soon to dismiss it as just a chat app as well.
So they have a platform that's going to shape the next generations social interactions for the worse [1], and can only barely monetize (and if they can monetize profitably, its for an audience with the least amount of purchasing power in several generations)?
Are you kidding? Advertisers trip over themselves for the chance to advertise to consumerism-drenched, trend-driven teenagers and soon-to-be twenty-somethings.