This makes a fair bit more sense when you realize that hierarchy and the resulting feudalist structures are basically the core tenets of right-wing ideology. On paper, the right should have a harder time working together: The fascists, theocrats, and kleptocrats have wildly divergent worldviews. However, more fundamental than any of their specific views, they all believe in rigid power hierarchies. Which means to bring one branch of the right into the fold of whichever group currently holds the most power, all they really have to do is win over the upper echelons of the weaker faction, and then secure them a place (not necessarily even that highly ranked of a place) within their power structure.
Meanwhile, across the isle, a vague alignment in short term goals is basically all that keeps the left and the liberals together as a coalition. Whereas the right can say and do just about anything as long as it doesn't jeopardize their direct underlings' position in the overarching power structure, even small, strategic concessions can obliterate what little trust leaders have built up over the years.