Because not everyone is the "economically rational agent" that just wants to maximize profits as much as they can. May be you disagree, and think most people are and it's strong enough to be a normal distribution. (I am not sure it is, but i sure hope it is not a normal distribution and there are enough people outside).
It doesn't matter that not everyone is a "economically rational agent". What matters is that there are some of them. People who will reinvest their profit into more mining, to profit more and reinvest it further. The people who are currently fabbing their own ASICs and setting up mining farms in places where electricity is cheap. These people left unchecked will, over time, suck up all spare electricity generation capacity and eventually outbid quite a lot of normal electricity use.
Once again I disagree.. these "some people" need to be the majority(of anyone participating in these currencies) for this mining to stay profitable.. Of course i may be mistaken about that part of the reasoning, but I'm fairly confident about it. Please let me know if you think it is an unfair assumption.
Ah... I am talking about who gets to determine the cost of the coins.. So I assumed it's majority of the people who use it as a currency or exchange. But then that's my default assumption about crypto currencies in general and not sure that applies to NFTs..
