Republicans feel that they are Republicans because of principles, and when somebody in the party is not espousing those principles, they are belying what makes them a Republican.
Democrats feel good about being Democrats - so Democrats can be pro-life, pro-gun, fiscally-conservative, strong on national defense...and you will not hear them called DINOs. It does not matter to Democrat politicians that our system of Social Security is a doomed Ponzi scheme. It does not matter to Democrat politicians that Medicare and Medicaid can not pay for themselves. It does not matter to Democrat politicians that the US Postal Service is costing billions each year. To Democrat politicians there is always another law, always another program, always another slogan to look to.
Not a single Republican voted for Obamacare.
There is room for diversity in the Republican party. It is hard to find a politician with which I agree 100% on the issues. But...