So in other words, you think they don't have a spec and they're throwing more bodies at the problem instead of fixing their process? That would be very short-sighted, but it could be possible.
Large consumer apps generally are iterative affairs where the engineers & designers have a big say in the final product. At any given time Airbnb probably has multiple cross functional teams building different features.
These teams are probably constantly testing and iterating the final design based on user research and testing.
At least that was my experience working at Facebook on their iOS app.
