Aaron Blake’s “Why Republicans have no incentive to compromise” at WaPo’s ‘The Fix’ explains it well:

…Republicans in Congress have very little incentive to come to the middle on the big issues before the country.
And a new poll from the Pew Research Center says it all: Quite simply, it’s because the GOP base demands principles over compromise…According to the new national Pew survey, 50 percent of Americans would rather that their elected officials “make compromises with people they disagree with” rather than “stick to their positions” (44 percent).
But when you break it down by party, you see the reason we have gridlock.
While 59 percent of Democrats prefer compromise to principled stands, just 36 percent of Republicans say the same (compared to 55 percent who want principled stands).
For Republicans, that’s actually up slightly from the 32 percent who wanted compromise two years ago, after the 2010 election in which the GOP reaped huge gains by standing resolutely against Obama’s agenda. But over the same span, the percentage of Democrats calling for compromise has risen significantly — from 46 percent to 59 percent. And independents have also moved by double digits toward favoring compromise.

In other words, the Republicans in Congress who refuse to compromise are not betraying a majority their supporters. They are reflecting the views of the voters who elected them, often in gerrymandered districts. All of which leaves the GOP in a bit of a dilemma.
As Blake concludes, “Their base demands that they resist compromise, but doing so causes the party as a whole to fall out of favor with the American public.”