I think it had something to do with credit card fees

Edit: found this on reddit

Grey Markets are often done by credit card scammers which results into chargebacks by the credit institute resulting in processing fees for the producer of the game or even getting them cc banned.

Edit edit: it was Factorio - https://arstechnica.com/gaming/2020/05/g2a-confirms-stolen-game-key-sales-pays-40000-to-factorio-devs/