I absolutely despise cryptocurrency, so this may not be accurate, but my understanding is that they’re only reliable if many independent people mine. If NVIDIA kept all its GPUs and mined Bitcoin instead of selling them, it could control more than 50% of the hashing capacity. This could allow NVIDIA to double-spend bitcoins, the possibility of which would probably crash confidence in the asset.
> they’re only reliable if many independent people mine
Sort of. It's a matter of establishing trust with buyers, holders, and the ecosystem. If a hypothetical 51% owner behaved as a good citizen (which is to say, their incentives were publicly aligned towards preserving value rather than exploiting double-spends), the confidence wouldn't necessarily erode. (Contrast with a nation-state or other hostile actor who performs a 51% attack with the express intent of theft or undermining trust, which has happened with smaller cryptos.)
The three largest BTC miners combined have been well over 51% of the hashpower for years now, and they could collude to crash or exploit BTC if they wanted; it's simply not currently in their interest. Yet more evidence that while Proof of Work was a clever hack in the original BTC whitepaper, it doesn't inherently lead to decentralization, and is functionally indistinguishable from Proof of Stake with extra steps.
