I assume most investors are smarter than that and are hoping AirBnB will build a monopoly similar to how google did with search and Wikipedia did with online encyclopedias.
A 5% monopoly tax on most rentals/hotels does give you a huge profit eventually.
Is there any paid service with actual monopoly yet? Amazon has market share, but also competitive prices. To me all of these big markets like taxi, food delivery and online booking seem rather low barrier of entry. And that the customers will be price aware. That can't be really compared with free services like Google, Wikipedia or Youtube...
The optimal shape for most markets is a duopoly. Both competitors get a large enough stake to continue growing, but don't really meaningfully compete, and don't have to worry as much about antitrust.
A 5% monopoly tax on most rentals/hotels does give you a huge profit eventually.