Of course, had Scalia been replaced with even a moderate justice, as would been proper, the issue would not be in doubt.
The liberal wing of the court is taking a more global view. In the case of Wisconsin, even though Republicans received only 48% of the vote, they nonetheless control the legislature 60-39. This isn't a case of gaining a slight advantage; it's a case of getting complete control with a super majority despite being the minority party.
It seems pretty clear that this is a case where the government, who controls the election process, has figured out a way to thwart the will of the people as reflected in their votes and ensure themselves permanent control of the political process of the state no matter how the people of the state vote.
This is so clearly an intrusion into the democratic process that it cannot be allowed to stand. Even the conservative justices admit it's an unpleasant state of affairs.
But the conservative justices are not concerned with the consequences of the states actions. They are concerned with the very narrow legal question of how to define exactly what constitutes gerrymandering -- how to precisely define what exact actions or procedures would is rise to the level of unconstitutionality. And since that is not something that has a simple answer, they are going to decline to interfere.
Their stance seems to be that yes, this is a very bad thing with serious repercussions, but unless someone can precisely define
exactly how it's being done, and propose an exact standard to prevent it, the court must let it continue.
Will Kennedy side with the liberal wing this time? Maybe so. He seems to have become a bit more liberal in the past few years. A bit more concerned with the real life consequences of Supreme Court rulings. But it's a very thin thread to hang ones hopes on.