Zvika Krieger proposes an answer in his profile of the Utah governor, Obama's nominee to be the US ambassador to China:
If Huntsman was planning to run for president, why would he move so brazenly to the left at a time when the GOP seems to be heading rightward? The most obvious reason is that he may actually be a moderate. "I'm not very good at tags," he tells me. "I just try to do my best, and maybe that makes me a pragmatist." He joins a long tradition of moderate Republicans from Utah, despite--or perhaps because of--the fact that the state is the reddest in the country, with the GOP holding every statewide office and more than two-thirds of the state legislature. The GOP lock on Utah politics allows the party to welcome a broader swathe of politicians, and breed leaders who are less combative and ideological than their besieged colleagues in more competitive states. And if Huntsman has learned anything from the failed Mitt Romney campaign, it is that the only thing worse for a Republican than not being a conservative is being a phony conservative.
Emphasis mine. If Huntsman does make a run for the presidency, the big question will be whether or not he will resist that GOP pressure to move right.