Because in Denmark, immigration can be part of public debate without being shunned, while in Sweden, it's hard to get any sort of ground in this debate without being labelled a racist.
So now, some of them are trying to be more 'reasonable' about it with the party Sverigedemokraterna. I assume because they haven't made any progress publicly in Sweden by just being seen as extremists. And more and more figures are beginning to tell Swedes that immigration is not an issue you can ignore, thus Sverigedemokraterna's support is rising, because it's the only party that wants to talk about it.
But I am confident, that most of its votes are 'protest votes', to get the other parties to talk about it.