They're cancelling her because of her conservative beliefs.
This, but unironically. Cheney is much more conservative than Stefanik according to the Heritage Foundation rankings, for example. It's mind-curdling to watch partisan Democrats come to the defense of Cheney in this instance.
Cheney doesn't deserve any defense, and I agree. And yes, any reasonable comparative ranking has to consider Stefanik more moderate than Cheney.
Stefanik may be a shameless careerist but I can hardly muster any sympathy for Cheney being thrown overboard regardless. She made her bed. Now she has to sleep in it.