Is there a big reason for the DPP strength?
The main reason is the meltdown of the social democrats. All the people disappointed with the governments fairly righht wing economic policies have got to go somewhere. A lot of people are going to the Red Green Alliance, but there are a lot of people who won't move that fa to the left. So they move to the right instead, probably figuring that the economic policies will be similar but with stricter immigration policies. DPP, being the opportunist that they are, have tried to position themselves to the left of the government on economic issues and they are being rewarded for this. However, the DPP will still support a Venstre government and will likely support that governments economic policies almost regardless of what they are like. Economic issues are not their primary concern - immigration is.