Mill stated above statement because he thought that it is better to be dissatisfied than a fool satisfied as dissatisfaction allow individuals to experience and/or understand lower and higher pleasures (pleasure forms) so that they can understand and enjoy their position (either its lower pleasure or higher pleasure) that's why Mills satisfied with Socrates unsatisfied version that can allow individuals to seek for their own pleasure and become knowledgeable to achieve a pleasure form unlike a pig or fool.