The occupancy tax is a tricky subject and might be handled differently from location to location. Some places require the renter to submit that tax direclty, at some location AIRBNB is collecting the tax. The logic behind the practice to keep taxes and remit them to the authorities even for cancellations is questionable though. It is not an " income-tax" based on the rental income, but a tax that is due if a foreigner is staying in the community and pays someone for it. To collect this tax with noone visiting the community seems a strange thing. Not sure that AIRBNB is with this in legal grey zone. Otherwise the logic of that tax would be that the "intent to visit" in the from of a reservation is taxable. A tax like this does and should not exist.
I had an example with a stay in Paris were I had to cancel, but still had to pay half the rental fee and the AIRBNB fee. In Paris the Occupancy-Tax is collected by AIRBNB and they did not refund that amount initially. After a couple of emails and contact with customer support they finally agreed to refund the tax and refund the booking fee on top of it - more or less as an apology.