Because the mining equipment is expensive and the duration of free electricity intervals are outweighed by expensive electricity intervals

Related: Bitcoin miner RIOT made $32 mln by reducing or being willing to reduce if needed — its energy use consumption.

https://www.texastribune.org/2024/01/03/texas-bitcoin-profit...

A company such as Riot also can profit by buying power at negotiated rates ahead of time — retail power companies allow big companies to lock in prices that way — then selling it back into the state market when energy prices soar during extreme heat or cold. In Riot’s case, when electricity prices soared during the summer heat wave, Riot sold power back to TXU, a Dallas-based electricity provider, which sold it back to the grid.

But if the value of Bitcoin is low and the cost of electricity is high, crypto companies can make more money selling power than mining Bitcoin. In August 2023, Riot reported selling 300 Bitcoins for a net proceeds of $8.6 million. Meanwhile, the company said it earned $24.2 million in credits to its electric bill for selling power back to the grid.

Metal foundries in Europe generally have dibs with large, long term power purchasing contracts. IIRC there's even some legislation that favours them since they're a national security resource.

I assume there are taxes and transmission fees on top of the spot electricity price