The filter cartridge works best at the early stages of the cytokine storm. At that time, the patient in the (Italian) hospital may have good chances of recovery without it. So relies on luck. The expensive filter is just an option and likely the Doctor is not even trained to use it, so it is less likely to happen.
Later, when the patient is dying like in the video link posted by KC it is probably not as effective.
Why price it at 1000 Euros? Intro price it at 30% min IMO (volume pricing extended because of crisis etc.) . Win a customer, not just a sale.