Probably tax credits and the need to shoot in European locations nearby for the war scenes. Since you live in Toronto, you're probably familiar with Toronto filling in for NYC for financial reasons. Apparently NYC is an expensive nightmare to film in. That kind of stuff is very common. They shot a Civil War flick in Romania once, or something like that. Boggles my mind that Tennessee is too rich for their blood but whatever...One thing, though; why are they filming in England instead of in the USA?
I just don't like the aesthetics of the Nazi bikes. I know maybe they're trying for "more advanced than the 1940s" look to make them look more fearsome, but there should have been some other way to do that. Not a big thing, tho.