The accountants wouldn't believe us when we told them that the machines were worthless after only 6 months.
We’re talking about significant 100x-1,000x improvements in efficiency and profitability.
To stay competitive, these improvements in efficiency made it necessary for miners to upgrade mining equipment every 3-6 months.
Because of its closeness to silicon fabrication and cheap energy, China emerged as the de facto place to set up these mining farms. Those previous 100x-1,000x improvements are no longer possible.
The development of mining hardware caught up with Moore’s law.
This is the observation that transistors in a dense integrated circuit doubles about every two years.
It would be fair to assume ~2x improvements in mining every ~2 years.
This would mean that mining equipment would now have a longer shelf life, and no longer be obsolete in a few months.
And we don't know if it's unique to his situation or for any miner at a certain scale.
Although most miners will know people who they can trade face to face with if they don't care about taxes and don't want KYC.
If the accountant's salary depends on being assuaged, this should hardly be a problem: the accountant will then just tell you that he does not believe this to be a good idea, and give reasons for his judgement.
In practice that would never happen because by the time miners are done with the cards they'd be too out of date for machine learning or other general compute workloads, and useless for budget gamers because of the lack of display outputs. It's really a shame how much power and silicon is being wasted on cryptomining.
But as you say, whether they'd be useful for rendering once their crypto-life is over is debatable.
Compute power is compute power. Everyone in the world wants more for their task.
Think of something as direct as a cell phone modem. The batteries last as long as they do because a ton of the low level modem behavior is done in accelerator blocks direct in hardware, and the DSPs just route data between the blocks and manage the higher level protocols.
If you devoted extra area to some other algorithm, it would be a big cost for no benefit. Put that logic on some other ASIC and buy that one instead.
In general what you want to do is design the algorithms differently. There's a few reasons to do this. Firstly your new coin probably doesn't want to run best on hardware which is already used by a bigger coin, especially bitcoin, because then there's a massive attack vector just looming over you as the existing miners could just turn a fraction of their processing power towards your network and destroy it easily. This means you generally want to come up with a novel proof of work function which is not easily computed by existing miners. The best form of this is using a completely different hardware resource.
Secondly (and apart from the few large coins which generally got to this idea first, competing with the first point), if you care about keeping your miners distributed in terms of ownership and control, it helps if said algorithm is tuned for some general purpose bit of hardware your users are already likely to have for some other purpose. Ethereum's PoW was expliticly designed to be optimal for GPUs (because computing it is memory-bandwidth limited), and Monero's was designed to be optimal for CPUs. Chia's system was optimised for storage space instead of compute power. Lower-effort clones (e.g. dogecoin) tend to at least change the hashing algorithm used at little to provide some protection, but to a lesser degree (e.g. Ethereum is probably safe from attacks by bitcoin miners, Monero is probably safe from ethereum miners, but while dogecoin is probably safe from attacks by bitcoin miners, it's not safe from the other larger coins, and especially bitcoin forks have actually been attacked by bitcoin miners).
(your last point however is valid nonetheless, the scenario of large blocks of capacity jumping between networks and how deliberate algorithm design tweaks might offer some protection)
The tools available today support such rapid design/test cycles.
I guess that explains why GPUs are so cheap and plentiful.
Or perhaps they're mining another crypto currency.
It's been over 7 years since mining on anything except ASICs is a guaranteeing a loss.
Most people are, but many major mining operations are not.
If power is free then any hashrate is profitable. With "typical" power prices you basically need ASICs. In the middle there are myriad possibilities, and many miners have access to very cheap power (eg during hydro gluts in monsoons).
As an example, the AMD Radeon HD 7870XT[1]. It gets 346 Mh/s for bitcoin, which is $0.00004308/day[2]. It gets 14.5 Mh/s for ethereum, which is $0.3508/day[3]. So you get 8000x more by mining ethereum.
[1] https://technical.city/en/video/Radeon-HD-7870-XT
[2] https://www.cryptocompare.com/mining/calculator/btc?HashingP...
[3] https://www.cryptocompare.com/mining/calculator/eth?HashingP...