Some centrists are, frankly, low information voters. They don't really have a conviction or do their research well. I love my friend and I owe him a lot, but he supported Trump because of the initial anti-war and immigration rhetoric. He's not far right, he supports Palestine and he's a Pole who despise the far right party that ruled his country for eight years; but he is one of the many single and lonely men who feels lost and doesn't have a direction. His background and profile are those preyed upon by the right, even if the person is of varying flavour of centrist.
The right don't really need to convince people to join them, they just have to sow enough doubt to prevent the left from being a coherent movement.