The definition of GPE for a mass at a point is 'the work done in bringing a mass from infinity to the point'. But when you bring a mass from infinity towards the gravitational body, isn't the work done always positive?

Sorry but I really don't understand why starting from the centre of the gravitational body is inapplicable.Actually, we can start from the infinite or the center of the gravitatioal body. It's only the difference between negative and positive values. If we start from the infinite, we can get an approximate feasible way to set out. If we start form the center of the gravitational body, we set out from a nearly impossible mission. In another hand, in the infinite the gravity is zero, if we take potential energy is also zero, then we feel more natural in logic.