They are willing to do what Democrats are not.
At the end of the day, a lot of Republican constituency groups are willing to go along with an all-or-nothing strategy on most issues, while Democratic constituency groups are perfectly willing to bargain for as much as they can get. Look: if you want universal health care, you are probably willing to settle for moving from 80% coverage to 95% coverage (or whatever the actual numbers are). If you believe that government involvement in health care is unconstitutional, or immoral, or whatever, then there's not much to bargain over. [...]
In lots of policy areas, Republicans simply don't care very much what happens. And while that has a lot of limitations, it also can at times give them strong bargaining power.