Why the Arctic? change of location question.

I think the Cold War/Russian aspect was part of it, but mainly I think it was because Hawks believed the change of Poles made the story more suspenseful in that Alaska is nearer the U.S. and therefore the alien threat would seem more "real" or "immediate" than it would in the much more remote Antarctic.

Changing to the Arctic also added to the plot point of being unable to radio their superiors in Anchorage due to the storm, yet still having enough sporadic contact with them that Hendry's efforts to combat the Thing were complicated further. In the Antarctic they would be in total isolation, which is suspenseful but not in the ways Hawks wanted for his variation on the characters and story. Also, because of its relative accessibility, the Arctic served as a better locale for the romantic and reporter aspects of the story, allowing the characters to pick up where they'd left off more easily, and so forth.

In the 50s the US was building a series of early warning stations in the far north, radars to detect Soviet ICBMs and bombers coming over the pole. It was widely reported in the news at the time, and several science fiction films "cashed in" on it as a way to have US characters off in a remote isolated outpost - the infamous The Giant Claw, for example. The whole "threat from the north!" aspect probably made it resonate with audiences who were seeing similar things in the newsreels.

There are good answers here. However, in 1951, Americans, in particular, were more familiar with the Arctic. It was reachable in the minds of common folks. Antarctica was so far removed from anyone's experience, but people were aware, however, vaguely, that even Inuit (Eskimo) people could live within the Arctic Circle.

And someone is correct: the proximity to Russia was likely a secondary consideration. In 1951, The Cold War is colding up--I didn't know how else to say
it--and school children were beginning to experience the dive-under-your-desk atomic bomb air raid drills. So everyone except the Rosenbergs and other Soviet spies, knew that Soviet Russia was the enemy.

In the Antarctic, perceived enemies would have been penguins.

Campbell's original story -- "Who Goes There?" -- involved a group of scientists doing research at the south pole. The story for "The Thing from Another World" brought the military in on it, and that can be woven into the story more convincingly at the north pole: the air force has relatively easy access from Alaska (it's still a major haul to get to the south pole); the sense of urgency is more palpable with the saucer crashing the night before the story begins, whereas in Campbell's story it's been there for a million years; the dog attack scene can be kept, since people link dogs with the north pole and Eskimos (which we never actually see); the romance element is more plausible; finally, the north pole is a lot closer to us than the south pole, and that kind of heightens the sense of alarm to the viewer. Very few sci-fi/horror films from that era were made without a romantic element, so that was an important consideration. No studio would have bankrolled a sci-fi movie about a bunch of men, and only men. Interesting to note, though, that the ship in the movie was a saucer, whereas in the story it was shaped like a submarine without a tower or diving planes. Campbell wrote the story before the phenomenon of "flying saucers" entered pop culture.

You can read the story "Who Goes There?" for free at a site called "Outpost 31", which is set up for fans of John Carpenter's version of the story.