Logistics, logistics, logistics
Germany? By the time they could undo the blitzing of the iron ore
mines AND get them fully running again WWII would be half over. Those
mines are waaay up in northern Sweden and could not be gotten to
quickly, esp. by the kind of troops the Germans had in Norway. Their
concern were the Brits.
Russia? Have to get thru Finland first. Different rail gauges and
one helluva diversion of resources.
Britain? Even after America came in nothing changes the fact that
they can't get to Sweden logistically. Both Norway and Denmark
present problems preventing entry. Norway doesn't have a single
major port except Oslo which is a shooting gallery for the defenders
against a naval invasion. Even the Germans in 1940 got slaughtered
and would have been driven into the sea if not for their
paratroopers. Copenhagen itself isn't as bad but getting thru those
belts/straights is worse.
And I haven't mentioned that Sweden's army wasn't much smaller
than Finland's, with a good rail network to get the troops where
they would be needed. How was their navy and air power?
All these facts were known OTL, which is why I think no one gave
Sweden a second glance.
By the way, is it true Sweden cut the Nazis off right after the liberation
of Paris? Not much the Germans could do by then.

What would it have cost Hitler if done early on? At the very least
a more anemic U-Boat War, Case Blue, and Kursk. Yes, let us
leave the swedes alone. They're not going anywhere...
