There are two unique userbases for AirBnB - renters and renters. Renters may not have a 20% daily retention but I would bet that rentees are much closer to 20%.
On top of that, AirBnB is a marketplace. I would imagine that marketplaces are affected more by supply and demand ownership than daily retention.
I was going to propose the exact opposite: renters who want to keep their ratings high go back frequently to answer inquiries while each individual rentee only goes on the site occasionally when traveling.
I chose not to use "owner" because not all people listing on AirBnB own their property, but I think we were thinking the same thing. People listing properties almost definitely have higher retention than travelers.
On top of that, AirBnB is a marketplace. I would imagine that marketplaces are affected more by supply and demand ownership than daily retention.