So the incentive to invade Norway should not be based on facts but what they percieved at the time?
I think that the Narvik rule in WIF, and MWF, is to strong. As it turned out, after the occupation, Narvik was not needed to ship the ore to Germany
And why is this on Germany? Why is it not on the Allies?
It's on both. Churchill thought "hey, if we invade Norway, we can stop those iron ore shipments. Let's invade!" Turns out he might have been wrong (although really all we can do is speculate). Germany thought "Hey, if they invade Norway, they're going to stop our iron ore shipments. We better invade first!" In WiF, the British player thinks "Hey, if I invade Norway, I might get lucky enough to stop the occasional iron ore shipment. Seems like a lot of risk for very little reward. I'll pass." and the German player thinks "Hey, if the CW invades Norway, it might cost me an occasional ore shipment, but I'll gain US entry benefits, free naval units, he'll lose some units, and I can still march into Oslo or defend Narvik. Don't let me get in your way, Churchill"