Power politics. Reinfeldt's bet in 2014 that the far right could be harnessed in a powerless position backfired when the Sweden democrats declared that they would vote for the opposing budget unless given influence on it, and the Sweden democrats then continued gaining voters on the right. To stem the flow the conservatives have accepted the far right and largely incorporated their rhetoric on immigration, and from there it is a small step to cooperation.

The liberal parties on the other hand has voters who are liberal on migration and anathema to the far right. The Liberals are now consistently polling around 3%, below the 4% limit to stay in parliament. Joining the right might be a desperate move to hope for support voters from the Moderates who switch to keep them in parliament to avoid the 3% being wasted. On the other hand right wing voters might prefer to see them gone.

The Center is polling well around 10%, much thanks to their position as right wing against the far right, but has real issues with dealing with the Left party.

The Conservatives might be counting on neutralizing the liberals by getting the Liberal party out or on their side, and the Center as passive support. There's a clear campaign from them to get rid of the Greens that are polling around 4%.

With the Christian democrats also polling around 4%, the election will probably turn on which of the smaller parties get 4,02% and which gets 3,98%. The 4% line is the closest we get to your swing states.