Since Conservatives and Liberals are in the minority, elections are won/lost in the middle where principles are not that clear cut. The first principle must be too win. Unless you win the election, your principles matter are worthless.
Most people do not consider government in the same light as do conservatives. There is no clearer path to losing the trust and confidence of the American People (and losing elections) than shutting down the government.
Is it winning when you have McCain Flake in the same foxhole as Cruz? They will try to kill Cruz as they showed they would. Would never share a foxhole with someone that would throw up the white flag at first sign of trouble aka Flake McCain Murkowski and too many more.