Having received training mostly as an economist, I wonder whether why
Utilitarianism makes the sum-total of happiness or average happiness the final end of human activity, what we should maximize.
Nearby competitors may disagree about the aggregation part, holding, for example, that we should maximize not the average happiness but rather the lowest level of happiness, or that we should equalize happiness. Or they may disagree with the happiness part (may hold, for instance, that love or knowledge have an importance that is not reducible to their contribution to happiness).
All such "consequentialist" views can be applied to human agents (to the question of how they ought to conduct themselves) and also to human societies (to the question of how these should be structured and governed). So utilitarianism is one of many consequentialist views.
There are also non-consequentialist views. In regard to human agents, there are views that guide them not toward making the world better but rather toward making oneself the best one can be (virtue ethics) or toward doing one's duties (deontological ethics). In regard to societies, too, there are non-consequentialist views, for example ones that give more weight to harms a society's rules mandate or authorize than to equivalent harms that these rules merely foreseeably but contingently bring about.
Rawls's theory is about how societies should be structured and governed. He is not a utilitarian; but I would classify him as a consequentialist: he holds that society should be governed by whatever public criterion of justice will best fulfill citizens' higher-order interests, especially those of the people whose higher-order interests are least well fulfilled.