I find it profoundly stupid for Airbnb to have their own typeface. It's like they have lots of designers around and have to keep them busy with something. Well at least they did not give them the usual entertainment for bored designers: redesigning stuff that does not need a redesign.
Creating a typeface which you own is cheaper than licensing a third-party typeface, at scale.
The cheapest fonts are the ones installed on a users system. Web sites and apps do not need to include fonts at all. In fact it's easy to argue that the users should be selecting the fonts on their devices in most cases.