> They could sell their cards in cooperation with Steam: Only people with an active steam account are eligible to a new card. If their performance stats don't improve after the purchase, which means they have resold their hardware, they won't be allowed to buy another card.

I have a baby. I do anything on Steam once a month at best. Crypto miners could pretty trivially make their use cases look like they spend more time gaming than a good 30% of Steam's active user base. This is a non-starter.