Why does everything have to be historically accurate?

There are two issues regarding historical accuracy in any work of fiction, science fiction included. One is the willing suspension of disbelief. If the departure from reality is not plausible enough, then people will not accept the premise of the show. If the work is otherwise well done, consumers can accept almost anything, especially if the details of the departure are not important to the continuing story.

In this case, even though it was not possible for the Nazis to win the war, winning the war is just backstory that we can just accept and go on.

Another reason to keep as much historical accuracy as is consistent with the setting is that it is sloppy writing and production. If they're sloppy there, then they've likely been sloppy elsewhere too and it will show. This show does not seem to suffer much from this, though I understand there have been some very minor lapses of the sort that are inevitable in any film or TV show.

Dave-R011's reply is probably the best your going to get.

I'll just add that there are a few reasons for some to find issue with this show other than nitpicking over historical inaccuracies.

For one thing, given the context of this story and the real-life existence today of white nationalists, there are people in the world that are not going to be happy with this show painting Nazi Reich world domination in not such a pretty light. Showing cracks in this fictional Nazi totalitarian system doesn't help their recruitment numbers.

Even so, there are posters in this forum who have openly claimed that the Nazi vision held by those in power (in this show) is the right one (details spared as they would contain spoilers for season 2 -- come back when you're done if you finish before these message boards close down on 2/20/2017).

RIP IMDb message boards!

It is not possible for a fictional story about the Axis winning the Second World War to be historically accurate.