Their social network and brand recognition is their moat for now. Hosts and guests trust Airbnb. An upstart will have overcome a lot of momentum to take on Airbnb in the broad market.
I suppose the landlords could port their reviews to a new platform by linking to the Airbnb listing similarly to how people used to post their eBay reviews when selling on forums. But yeah having all those reviews viewable natively for comparison is nice for renters.
