Because Voldermort expects the prophecy to become a reality if all the conditions it states are met, e.g. hermione dying. It doesn’t matter how he tries to thwart Harry, as long as Hermione dies the prophecy will be fulfilled and Harry wil end the world. He believes this strongly because he’s tried it before himself and there is plenty of lore of it happening before.
Because Voldermort expects the prophecy to become a reality if all the conditions it states are met, e.g. hermione dying. It doesn’t matter how he tries to thwart Harry, as long as Hermione dies the prophecy will be fulfilled and Harry wil end the world. He believes this strongly because he’s tried it before himself and there is plenty of lore of it happening before.