Did you issue the payment from your account a service? Did you issue it from a hardware wallet? Did you, by chance, happen to decide that you want to use an anonymization tool when buying your exploit? Perhaps, you have a strict retention policy and destroy keys which are no longer used and can't sign for it anymore…
If you are paying 20btc for a zero day exploit I suppose you know what you are doing.
Either way everything you had mentioned are not deficiencies of Bitcoin per se.
This is one of multiple reasons why the Bitcoin system wasn't designed for people to reuse addresses.