Why don't the Social Democrats and the Moderates form a grand coalition?

Sweden has only had one grand coalition government in its history, a wartime national unity government that lasted from 1939 to 1945.

So why can't the two leading parties on both sides of the Swedish political divide, the Social Democrats and the Moderates, cooperate at the national level today?

Listen as Johan Hellström, associate professor of political science at Umeå University and an expert on Swedish bloc politics, explains what's preventing the two parties from joining forces. ...