It's really simple but it seems impossible for many to understand.
The hens are his hens, not yours. He's the boss and quite rightly so.
A rooster attracts hens in feral/freerange conditions by providing treats for his hens.
As far as the rooster is concerned you are trying to attract his hens away from him.
A roosters life without hens is a very very sad life. It's what roosters live for; hens.
A rooster will die for his hens if necessary and having you turn up with treats is competition he just cannot match. Often in such situations this feeding of the roosters hens produces aggressive behavior in the rooster towards the human that supplies the food.
Give the rooster the food and back away and let him call his hens to eat.