Crypto Mining Profitability

Mining is only profitable when the block reward and transaction fees are worth more than the costs of mining (electricity, capital costs). ETH was the only coin big enough to support all those GPU mining rigs. With ETH gone, there are too many miners and not enough valuable stuff to mine.

The cost of electricity skyrocketing and causing mining to no longer be profitable maybe?

You're forgetting about difficulty adjustment. Every time mining gets more expensive large number of miners drop out. This causes the difficulty target to drop. The remaining miners then start mining more blocks and profits rise. As a system it has built-in economic incentives to keep in in homeostasis.

If bitcoin price continues to rise, wouldn't the power cost become relatively smaller? Wouldn't miners care less?

This is the point of transaction fees in bitcoin. Fees get 'attached' to the block that is mined and go the miner. So even when all bitcoins have been distributed there will remain a profit motive for mining. The difficulty in mining is also automatically algorithmically adjusted, so if the industrial scale miners move onto other things - suddenly it might become profitable to go back to GPU mining. And the fewer people mining, the more profitable it would become.

Profit from mining (for example Bitcoin) does not scale linearly with the amount of money you put in. If only a few miners control the hash power of the network, that will discourage use of the currency and drive the price of it down. It's not in the interest of miners to control > 50%.

That's helpful, thanks. Still, it's only profitable to mine bitcoins at any computing cost if they can be exchanged for other items of value. If the value of bitcoins drop and people leave the bitcoin economy, making the last N bitcoins easier to compute won't make them more valuable.

This is wrong argument. Mining costs are different for different miners. Someone has cheap electricity, someone has cheap electronics. If mining is not profitable for some part of miners, they'll stop mining and difficulty of mining will decrease, making mining more profitable again. It's a self-regulating mechanism.

Mining isn't free. You need to pay for space and power (especially when we're talking about the large scale miners capable of making an impact on the hardware supply). With most bitcoin like coins, the hashrate of the network has diminishing returns as the difficulty increases and the amount of compute resources needed to mine blocks at a decent rate increases. If your computing capabilities are worse than your competitors, it's unlikely you'll make a profit (which is part of

if the value of a bitcoin was worth less than the amount to mine it everywhere in the world, why would people continue to mine?