Because the opinions had not been corrected to reflect which was the dissent and which was the concurrence!
See my June 2012 thread before I knew how to thread:
(How do we go back and find the original slip opinions before they were corrected?)
@_John_Mikhail @NeilScottSiegel
(Again, these tweets are from the day the decision came down. Some of us immediately knew Roberts had flipped his vote)