Rational from the POV of investors looking to extract some short-term returns. Completely irrational in that nobody seems to give a shit about Gamestop and they're actual performance as a business.
I have a guitar that I could sell on the open market for ~$300.
But I don't want to sell it.
If someone offered me $300 for it, I'd say no. If they offered $400, I'd still say no. I'd say no at $900.
Why? Because I don't want to sell it and I don't have to.
There is some price that will change my mind, of course, but it has nothing to do with the actual value of the guitar.
Most of the time the future is years down the road, because you made a good bet on what business would be profitable. Sometimes the future is the following Tuesday because someone got out over their skis and _needs_ your stock now.