If a democrat in those states voted for Trump in 2016, it was almost certainly because Trump pledged to bring jobs back to the US; so what would inspire those same people to support Kasich in 2020? What has the Mailman ever done?
He would attract those who are inclined towards nevertrumpism, and a lot of those idiots who talk about how much they dislike Trump’s style. It would keep them “pure” to vote for a guy like Kasich, who is nominally Republican but not Trump. There are people like that out there, I see them on social media.