Maybe to encourage longer stays? The cleaning fee is paid once per stay, not once per night. I get why it is a separate charge, since they aren't cleaning the place daily (like a hotel), only at the end of your stay.

It is a dark pattern causing the advertised rate to be lower so the listing will get included in more filters etc.

[edit] I checked and they changed this in April of 2025, as of then the fee is rolled up in the advertised rate.

For us, we charge the same cleaning fee whether you stay for 1 night or 7 nights. So I don't know how we can incorporate that into the nightly fee without either over-charging or under-charging for cleaning. Having it listed separately keeps it consistent and clear to guests.

My father runs a few guest suites and he explained to me why the cleaning fee is really helpful in terms of keeping a room's price reasonable per night but him not getting a bad deal for a single night guest.

The more often you wash linen then the faster it wears out and needs to be replaced.

While he has a cleaner who daily makes the bed and does basic cleaning (labour is far more affordable in South Africa), on checkout rooms need a more proper clean with additional use of a cleaning detergents.

Without a cleaning fee which is charged per stay, you'd have to increase the per night fee to cater for single night guests.

With the cleaning fee he can still keep per night rates as low as possible with single night guests still covering their actual overheads.

That was entirely on Airbnb for presenting it that way. Hosts would enter in their per-reservation cleaning cost so it could be integrated into the price paid by guests, but Airbnb stubbornly itemized it on the checkout page for years. I believe they finally did away with it (in favor of building into the nightly rate) about a year ago.

In some locales, it is included

Because this way they can lie to you and offer low rates to pull you in until you go to check out.