Shut up pleb, workings of Lord Nolan are beyond your comprehension.

That dude has always been able to spend a ridiculous amount of money on practical effects. Robin's cabin, from the movie (Insomnia), was built in the middle of the lake on one of Canada's most protected national parks. He spent a massive chunk of his budget on this one set and it involved hiring specialized construction workers, who were also professional divers, and they build almost the entire thing by hand. Since they had to make sure everything was in it's original shape when they left (they would be fined if the government even found a toothpick leftover), they were so meticulous with their tear-downs that it took a month... of full-time specialized crews, all disassembling the set by hand. All for a set that could have been just as beautiful if it was shot a half-hour away so he didn't have to follow all those rules. But he just wanted that one, specific look so he spent the money.

https://old.reddit.com/r/Filmmakers/comments/18ekbit/has_anyone_worked_with_christopher_nolan_and_how/kcqvcu2/

Its subtle world building for immerssion, as corn is all that will grow theyre growing it in places that didnt normaly have cornlike in the mountains. Hope that makes sense.

Yeah, or maybe you could edit in the mountains in post production.

I guess, it somewhat limits what shots you can do. And maybe, this would actually be more expensive, if there's lots of mountain shots...?