It's because like I said, Americans don't really know what "Christian nationalist" means. To a certain type of voter, that sounds like you're calling them men of God and actually just makes YOU look bad. They don't know what authoritarianism means either. Putting "right" or "right wing" in anything just sounds like "Republican."
But they sure as SHIT know that "nazis" and "fascists" and "Hitler" and "antisemitism" are BAD.
This ain't fucking complicated. You're just coward ass losers.