Well like every tech company the entire purpose of an externally facing engineering blog is to maximize their "tech/employer brand." That's the whole point. I would also guess that some of the projects highlighted are could probably fit into "complexity for complexity sake" e.g. teams of bored or overzealous engineers who are trying to justify their jobs by working on complex things that are probably overkill for the actual problem their trying to solve. That's pretty common.

I'm just pointing out that the nature of Airbnb's business means that there's no real-time, no streaming, no billions of concurrent users, etc. The tech boils down to a 1) web app 2) payments mechanism and 3) messaging. Nothing particularly revolutionary on the tech side.