Avik Roy lists reasons. His final point:
Health care policy is not a classical conservative concern. Romney, having made health-care reform the top priority of his governorship, knows the ins and outs of the issue in a way that no one else in the field does. The prominent Republicans who could have given Romney a run for his money — Mitch Daniels, Paul Ryan, and Bobby Jindal — aren’t running. Newt Gingrich comes closest to Romney’s health policy heft, but Gingrich has his own checkered history on the issue, and has generally stayed away from attacking the other candidates.
It’s hard to see how this dynamic changes between now and January. And given Romney’s strengths in most other policy areas, it’s hard to see how the race changes if Romney’s rivals can’t make health care an issue.
Pete Spiliakos agrees.
The Dish 