Because they know if they do it will be the end of their careers as professional "conservatives". So they clutch at any straw to cover their support for Crooked Hillary.
We are not so stupid to believe their assertions of doing this to ‘save’ the Republican Party or the country. They are doing this strictly to protect their influence and power in DC. As long as they are safe in their DC ivory towers, the country could burn and they would not care one bit.