I have an explanation. DJT has so changed the Republican base that DeSantis conservatives and their message aren't popular. Ronald Reagan was the last successful conservative president, and he was elected 43 years ago. Trump isn't a conservative by most measures, and that explains his popularity.
The America First message is the same message that Reagan articulated. Less Government, no forever Wars, and helping the working and Middle classes. It was just lost in bushwood for all the many years between Reagan and Trump.