A 5% monopoly tax on most rentals/hotels does give you a huge profit eventually.
Which ones will work and which ones won't is hard to tell, but that is indeed what investors are betting on.
At least Airbnb has a business model that could theoretically make it to profitability. An alarming number of these don't have any coherent path.
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...