Block magnets are square, rectangular or cubed. They have excellent surface area for maximizing pull force. While still remaining thin and minimizing weight.
Thick magnets such as cylinder magnets given their weight are not as effective in providing pull force as block magnets. Their thickness does not increase pull force in comparison to the thinner block and even disc magnets. The surface contact area is the critical factor in the utility of magnetism. The more surface area the more magnetic effect.