Why not?

The Trumpoids march in lockstep with each other, repeating the same, predictable, consistent lines.

Dems don’t. Dems have deep and very heated disagreements over issues that most Americans don’t care about, or care about but don’t understand, and are frustrated that the issue is complex and not solved by saying “I solve it”.

To an inattentive observer (ie most Americans), it looks like one side has all their ducks in a row and the other doesn’t.

Add in a dash of long-standing racism, sexism, homophobia, transphobia, and a very “Me me me” attitude towards foreign affairs, and you have the American electorate.

Why wouldn’t they believe this?