Why is Hollywierd doing a fantasy about America in need of rescue from the Nazis — when we are genuinely in need of rescue from the Communists?
It's a classic SF novel.
You might as well ask why make the Martian invasion story "The War of the Worlds" into a movie when we have enemies here at home.
It's entertainment for one thing.
There's also an intriguing "counterfactual history" angle that you don't get in movies or novels about the present-day.
There are plenty of parallels between our present administration and the Nazis.