AirBnB is/used to be cheap. People want cheap. They don't want to pay $200 a night for a hotel room when they travel to Paris, AirBnB knows that so I think they are much more concerned about the size of their inventory than the satisfaction of the guest or their reputation.
What fascinates me is the ability of most of theses "start-up" to successfully straight out ignore local laws, with very little consequences, and manage to put all the burden of legality onto their users.
They must have very good legal teams that exploit the flaws of legal systems. Talking about Paris, the great majority of listing are outright illegal, or at least used to be. If I were to set up a similar operation on my own, in France, I'd be shut down in a heart beat for providing illegal hotels and rentals and go straight to prison.
These people seem truly untouchable.
That's the strength of these services.