hah! you beat me to it. The energy cost is quite a big part of it, but also the hardware costs. These operations are hardly professionally run and accounted for. Most are prospectors and not businesspeople. Instead of amortized guess expensed immediately.
I'm with you on $20k+ per coin as theoretical NTA.
However, it is an NTA with no real value. Merely a hypothetical one. For a better description of the $20k+m try "sunk cost".