> No one is producing Bitcoin at loss, because it doesn't make any sense

The cost of producing bitcoin is a combination of the marginal cost (running the miner you already have, i.e. mostly power) and paying for the miner that you bought.

If you buy a miner expecting a certain profitability but then the economics change, you can both end up with a loss long term (never able to recoup the cost of the miner) and still be better off continuing to mine (because the cost of the miner is a sunk cost, and as long as the revenue is larger than the marginal cost of running it, you'll at least recoup some of it).