"conservatives" in a judicial sense these days more than their counterparts on the right. It makes a lot more sense that they would vote together -- they are voting NOT to strike down laws as unconstitutional on dubious grounds, NOT to reinvent the Second Amendment to undermine gun control, and NOT to reinvent the First Amendment to call corporate spending political speech.

I think your argument would be stronger if the roles were reversed. You also are forgetting that the three women are the ones who vote together >90% and the same is true of all the conservatives other than Kennedy (even Roberts). Breyer is not as "lock step" with the rest of the voting bloc as Kagan, Sotomayor, and Ginsburg, and probably is the most "liberal" among them.

Also not to belabor the point but the ENTIRE court votes together around 60-70% of the time. Most issues are not politically charged.