Mining at current prices is a $5 billion a year industry, mostly run on specialised chips at scale. Dorm room miners aren't a significant factor.
Regardless, there's also capital expenditures on the equipment.
The problem is that the price is so volatile. As with any industry, new entrants will keep joining in until total cost will approach total revenue. But if total revenue can just drop by 50% in the span of a few months, that can put a large portion of participants out of business, even if hypothetically one of their cost factors (electricity) is free, some participants will have to go.
Regardless, there's also capital expenditures on the equipment.
The problem is that the price is so volatile. As with any industry, new entrants will keep joining in until total cost will approach total revenue. But if total revenue can just drop by 50% in the span of a few months, that can put a large portion of participants out of business, even if hypothetically one of their cost factors (electricity) is free, some participants will have to go.