So I'd wager it's because by and large a lot of the established republicans hate trump as he's not one of them (the established party grandes) but an outsider who took over the party in essence
That was in 2016. Trumpets threw about the term RINO and moderates were forced to get in lock step behind Trump.
For the most part, they did. Several kept their councel but didn't stand up to him.
Then Jan 6 happened.
Trump didn't call off the dogs for hours as the capitol was sacked with every elected member inside.
There was a noose erected and chants to execute his vice president.
People crapped and peed in the halls of congress. They smashed windows, broke doors, stole artifacts.
They broke in to offices and thrashed them calling for the death of the speaker.
It was so far beyond the pale.
Imagine if this happened in the house of commons with every MP in attendance and the PM was in Downing st. letting it happen.
Now 40 of his 44 cabinet picks wont back him. His VP wont back him. His top military appointee says he's the most dangerous man around, his chief of staff called him a fascist.
By and large established republicans really hate him because he tried to overthrow democracy by force. He attempted a coup and failed. He should be in prison not MSG.