Pretty simple reasoning, a bitcoin miner can make a profit even if the price stays flat or it goes down, while you holding coins you can't unless it goes up. Same with stocks, you can make money while the price is going down, and even gain comparable to the bitcoin price in some intervals.
For example, MARA was 2$ in October 2020, it's $8 now.
Bitcoin was ~$11 000 at that time it's ~24 000 now.
It also peaked at $75 so with the same timing you would have experienced better returns than just buying and selling BTC
They are, they have around 7 Exa with around 12 Exa waiting for being put online by the end of Q1, so around 4-5% of the global hashrate.
LE, fixed the wrong quote, damn tabs!