Except it's not a gold rush. We know exactly how many bitcoins will ever be available. It's a scarce resource. Therefore, it's not unreasonable to buy and hold bitcoin in any amount.
Also, buying stock in GPU companies (putting aside risk of whatever their other business segments are doing, bad management, bad accounting, market risk, etc) implies that you think crypto market caps will expand (if mining is more profitable that imolies price has gone up). If that's true, why not just buy the bitcoin?
Yes it turned out to be, but did we know it at the time? If you bought gold during the CA gold rush, how did you know there wasn't 50 million tons of it waiting to be dug up? Turns out you would have done just fine buying gold in 1850. Bitcoin's supply is definitely limited.
