This is exactly the point... Airbnb does not actually hold a security deposit against their card, so by definition IT IS NOT A SECURITY DEPOSIT!
airbnb really needs to wither make it a true security deposit or call it something different. Until then it’s deceitful and misleading at best... Fraudulent, criminal and negligent at worst.
Either way, a host will quickly realize that the deposit really means nothing once you actually have to try and get it. Damage caused by guests or additional expenses such as extra cleaning/deodorizing of home due to smoking/marijuana/drugs/animals must be accepted by the guest and if the decline you are likely going to be at a loss... both for words and money.