This diagram show the full flow of the attack: https://miro.medium.com/v2/resize:fit:1400/format:webp/1*by4...
Because reads from blockchain are "free" (meaning, there is no cryptocurrency payment required to read data from the smart contracts on BSC), this is effectively free storage/hosting for the attacker.
The malicious code is served by BSC web API. According to the Krebs article, BSC "is aware of the malware abusing its blockchain, and is actively addressing the issue." I am not clear if they are taking this situation Very Seriously(TM), but I assume they are.