Because most of our digs are in private homes, they represent a significant saving over hotels and guesthouses but because of this, the relative cost and effort to receive a one-night booking (changing sheets, arranging keys etc) can prevent some Hosts from wanting to receive bookings for just one night.
The Hosts have an opportunity to select a minimum stay for the bookings they receive but some choose to charge a higher nightly rate to make it worth their while.