Ah, but it is likely that the deal is locked in place with some kind of price guarantee. Meaning they've guaranteed that they'll buy for 20 years, and in return they get a certain price. I doubt they've managed to get it for a flat price for 20 years, but it's likely a curve that'll be beneficial to both parts of the agreement.

And then any other parties not part of the deal that also need this gas, those who don't have 20 year contracts on fixed prices, they get to carry the burden. :)