Hydrogen fusion plants would produce helium in the reaction, which would need to be constantly filtered out.
Would be nice if that was the reason.
But not nearly the required amounts. We currently use about 6 million metric tons of helium per year.
If fusion plants ever become a commercially viable thing (and that’s a big if), they will never be able to supply anything close to that.
According to this, the anual production is 160 million cubic meters, which at a density of 0.166kg/m³ would be over 26 million metric tons of helium per year.
https://www.statista.com/statistics/925214/helium-production-worldwide-by-country/
If we currently only use 6, that’s 20 too many being produced. It would also seem like China is 95% dependent on helium import, so the US selling its reserves could be a reasonable way to level the import/export balance.
I got the 6 million from this link: https://www.chemanalyst.com/industry-report/helium-gas-market-578
The issue is not how much can be produced right now, but the rate at which we are depleting it.
I found different estimates on how long earth’s helium supply will last, and most of them are between 10 and 100 years. That’s not a long time, considering that it means we will lose access to a whole element.