1. AirBnb is a global market place. It’s much more difficult to build a global market place and its much easier to defend your moat once you are a global marketplace. Travelers from all over the world want to visit all over the world. There is a chicken and egg problem when you start. This benefit applies to Uber to much lesser degree because they are a city level market place. Most riders ride in their home city majority of their time.
2. Repeat business between travelers and hosts are much lesser compared to other gig economies. While people might get tempted to cut a direct deal with their cleaner or dog walker after a few good experiences, it’s much less likely to happen with AirBnb. Same benefits applies to Uber.
There wasn't a very good company to do all this through in anything like a consolidated way before. There were some vacation rental companies but none were very good. My parents rented out their vacation home in Mexico for many years and would absolutely have used AirBnB had it existed at the time.