Why would it seem like a much better strategic move than invading Russia? They are extremely different propositions, it seems to me.

It proved true that Sweden did not need to be invaded. It continued to supply trade and needed resources (mainly iron), and not invading it had advantages such as having a neutral country nearby, which is useful for other sorts of trade and politics. Also, invading and occupying a country requires time and many resources, and can have various negative results, both immediately and indirectly.

From a purely military perspective, since France and England declared war on Germany when they attacked Poland, Germany decided to address that threat as quickly as possible, which they felt required securing Denmark and Norway first, to avoid being outflanked by a naval invasion while they moved against France. (Hitler had hoped France and England would remain neutral even as he went on to attack Russia; Russia was the opponent he was always most concerned with.)

The schedule of attacking Denmark and Norway was something that had to be done quickly in order to have time to redeploy for a crushing attack on France and the Low Countries (and Britain) as early as possible in 1940. Attacking Sweden after Norway would have been even more effort than Norway, and probably would have delayed and weakened the attack on France, for little or no immediate gain or even reason. The reason for attacking Denmark and Norway was to be able to defend the coast against invasion, while Sweden offers no invadable coast if Denmark and Norway are held.

Once France had fallen, again there was little reason to attack Sweden, but there was a similar rush to consolidate eastern European countries before moving on Russia in 1941. A common criticism of what Germany did was their effort to help Italy in Africa, which delayed the invasion of Russia. Invading Sweden would have similarly tied up forces and further delayed the invasion of Russia, but again would have had little or no reason and negative results, as well.

Even if there was seen to be a reason to attack Sweden, it would have been greatly outweighed by the competing military need to hit France and Russia as soon and as strongly as possible, to prevent them from building up defensive positions or going on the offensive themselves.

This situation has been clear in all of the World War II strategic wargame representations I have played, such as *Third Reich*, *Hitler's War*, or even the simplistic *Strategic Command*, all of which do let you invade Sweden for an advantage to production, but also in all of them, it's almost certain that doing so will mess up your ability to deploy quickly in strength against France and/or Russia, which is pretty clearly more important.

In some games, invading Sweden also tends to make it more likely that the United States will declare war on Germany (and start war mobilization) earlier, which is of course also a very bad thing.

As for why Sweden vs. Russia, Hitler and Stalin both anticipated eventual war with each other, and Sweden had no plan to fight Germany, and massively fewer resources with which to do it. The only way that choice makes sense to me is if you could find a way be sure to never have to fight Russia at all, which would have been better, but probably wouldn't involve attacking Sweden to achieve it (though it might involve letting Stalin invade Finland). That would require a very different mindset than actually existed, particularly while Hitler and Stalin continued to rule.