Not downplaying the landlord's unlawful acts, but they couldn't have easily operated at this scale without the help of a popular platform.
There's also a 14% occupancy tax only on rentals of less than 30 days, so SF has a financial disincentive against converting all these properties to long term rentals. (Edit: if airbnb is lowering the average short term rental price, then the picture is less clear. There are tourists who will go outside SF if there aren't any 'whole house' options there...)