Counter offer... the turnaround time is locked in, cargo unloading and refueling, but fewer tasks mean fewer crew members needed to perform those tasks in the given time. So rather than 5 cleaners descending on an arriving plane, they can put 2 or 3 on it and pocket the 2 salaries they are no longer paying.

Just an offer, I don't actually know the airlines' historical cleaning crew requirement number trends.