But, as another commenter said, they can be used as a way to encourage longer stays, as with most places you only pay a single cleaning fee regardless of the length of your stay. But, again, it's just a fact that these rentals are usually just cleaned between guests (as opposed to a hotel when cleaning is done daily so it can be rolled into the nightly rate).
How much should the price increase per night to cover the cost of cleaning?
So either too low for people staying one night or too high for people staying multiple nights. Why is it better?
Averaging
No it can't because the hosts are trying to charge a fixed fee per reservation.
AirBnb hosts have had their hands on the scale for too long now because the company is terrified of a mass exodus of hosts (many of whom act just as entitled as your average landlord, who will beat every penny out of you). It used to be a much better service for the users.
At least last time I booked on AirBnB it was clearly displayed as part of the total reservation price if you entered dates.
Oh right, averaging.
And a less charitable interpretation is that it's a scam because it's deceptive advertising to show a lower nightly rate.
I'm willing to pay a cleaning fee (though really it should be rolled into the cost of the stay) but not also be required to do the cleaning myself.
If you can't efficiently get cleaning services for your rented out room, maybe you should get out of the hotel business!