Your story is not uncommon. You have to do everything exactly right, and at the right time, to even have half a chance at a successful claim against the “security deposit” that isn’t a real deposit to begin with. First, you have to contact the guest to see if they are willing to pay. If they aren’t, you have to take and submit dated photos, invoices, receipts after the guest leaves, but before the next guest arrives. Even then, if you get the wrong CS agent, and the guest says it was like that when they arrived, you may need a “before” photo.
There are probably other stringent requirements as well. And even then, CS can say no, and that’s it.
I’ve never bothered to try to collect on the Airbnb security deposit, and don’t plan to, especially for small stuff. I have talked to guests directly, and half of the time we have been able to come to some sort of payment agreement. Surprisingly, some guests are actually honest and apologetic.
Every host is different - there are hosts here that go after all damages, no matter the extent. Some even have the right formula, and have said they were successful every time they have tried to collect. Maybe some of them will post their methods here.