It's not being priced according to the long-term cost or capability of supplying the volumes that are being drawn from the stockpile on a sustainable basis, which is what you'd actually do if you were running a business dealing in actual production.
Yes, clearly all the people investing THEIR OWN MONEY are complete idiots, and you, a random guy on the internet, are so much smarter than actual investors and professional geologists. So does this mean you are going to invest all your money in helium futures, that are obviously going to be worth billions when the helium runs out, just like all the arm chair doomsayers are predicting?
Will you take the futures option the other way? That the current prices are going to stay at the level they are for say, the next ~20 years plus or minus 10%?
I don't know who you think is investing in this. People are just buying helium because they need it. The smart people are investing in gas mining because that's always profitable, and the big companies building huge helium liquefaction facilities are absolutely betting the price is going to rise in the near future.
Apparently the free market thinks you're kind of an idiot about this.