Well, let's put it this way. It probably wouldn't have made its way into womens' body-chemistry/psychological makeup to value men who are "good-looking" (whatever that means) if it hadn't been true, somewhere along the line, that women who had this value ended up more likely to pass along their genes, than women who didn't have this value.
Why would women who valued "good looks" have been, at some point, more likely to pass along their genes? Let's remember that in this discussion "good looks" is taken to be synonymous with "not mean-looking" and the opposite of "having long teeth and being able/willing to fight off rivals". So that gives us some guesses:
-maybe those who didn't prefer the "non-aggressive" mates, but rather were equally happy with the "aggressive" ones, got murdered by their (generally more aggressive) mates more often in violent rages, accidental bitings, etc, and thus had less of a chance to reproduce.
-similarly maybe the "aggressive mate" women had their offspring murdered more often..
-maybe those who stuck with the "aggressive" ones, ended up in large harems (since their mate was fighting lots of rivals and taking their mates..), which meant having a mate less likely to pay attention to their offspring in particular, leading to a higher infant/child mortality rate among such women
-meanwhile those who selected "less aggressive" ("good-looking") mates, were with guys who were less able to obtain and defend large harems through fighting... thus had more attention paid to them and their offspring... which as a result made it into adulthood at a higher rate.
So the point is there could indeed be some evolutionary advantages to having, say, brain-chemistry which "prefers good-looking men" as "good-looking" is defined here. And, the original appearance of that brain chemistry need not have some "evolutionary reason" per se, but could have just been a random thing. Like, in my guess #3, the females who first liked non-aggressive mates wouldn't have "known" that This guy will make a better father. She would have just been delighted by the guy's looks by internal factors.
At least that's how I understand evolution-type-stuff.