We used AirBnB extensively in the past for our trips accross Europe with the kids, camping isn't always an option, especially for city trips. Not sure when, but at a certain point Booking.com just surpased AirBnB with selection, availalability and price, plus it does include hotels and the like. In some regions you find tons of options on bookong and basically none on AirBnB, Iceland is recent example where AirBnB was mostly useless.

Maybe those two things are related, AirBnB searching a nieche to occupy with more "exotic" options. After all, hotels didn't go away, did they?