Although some may disagree with me, the difference in making love and having sex is emotion. Making love is an act shared by two people who have an emotional attachment and commitment to each other. When you love someone, all of the emotions tied to love: respect, caring, gentleness, kindness ( and so many more) are shared during sex.
Having sex is more like “hooking up” where sexual tension and pleasure are just that, a release. It is not to say that couples may not care about each other, in casual sex, they have not reached that deeper commitment that goes with loving someone.
Hope this helps!