Moreover, hosts told us that there have been recent regulatory changes and new registration requirements which seem to have had the effect of limiting supply.
I suspect they think it might be community-unfriendly and/or complicate the service.
As far as surprising places where AirBnB is hard to book - I'm surprised Boulder, CO isn't on the list. For as tech-heavy their city is, I recently went for a short consultancy there with a startup and found it nearly impossible to find any airbnbs anywhere. I think there were 3 with some availability in the whole city.
To my surprise, AirBnB is very eager to send refunds for bad experience, instead of concentrating on removing the bad hosts and guaranteeing a minimum level of quality. I really hope that they will work harder on this, because if a first-time user tries their service in SE Asia, chances are that he or she will never consider them again. Booking and the like are far more reliable in that region.