Airbnb seems like a terrible choice for last-minute booking because it's based on the notion of hosts responding via email in their spare time. When you book a room in a hotel you have reserved a room and don't need to do anything more except show up but when you book a room via airbnd you have merely made an inquiry and won't know whether you've reserved a room until you possibly get an email back after some non-deterministic amount of time.

Selection bias says the most responsive hosts will get booked early so the bookings that still show as available at the last minute tend to be less responsive hosts. A room that's still showing up as available at the last minute might be doing so because the host went on a hiking trip and forgot to update the calendar rather than because it's actually available.