Because Trump understands that Oz can win the state. He’s he closest to MAGA that can win. Barnette is an almost certain state wide loser.
You are brainwashed by the left and RINOs who hope you believe a true constitutionalist is "unelectable"
Trump was believed to be unelectable as well.
If horrible people like Ted Kennedy, Blumenthal and Sanders can be considered "electable" then good people, like Barnette, should be considered electable.
It is people like you who elect RINOs because you are afraid to lose on principles.