It's definitely the vibe. A lot of it is how the space is decorated. The random assortment of furniture and other stuff in an AirBnB contributes quite a lot to the atmosphere people are looking for.

But there is a psychology to it that is, as you say, hard to pin dow. A hotel that has a random assortment of plates and cutlery in the kitchen (like my last AirBnB did) would feel cheap and tacky. The AirBnB didn't.