Which is a nice way of saying they just made it up.
If you’re waiting for science from the social sciences, please take a number.
No, it isn't "made up," it is deductive reasoning based on a number of established factors.
First, woman is unique among mammals in that she is the only female who has permanently distended breasts and experiences "concealed ovulation" (no visual signs of being in estrus).
Second, man has the longest childhood of any animal (followed, in order, by elephants and orangutans). Which is significant because this allows for the human infant to be born in an extremely immature state (which goes to less trauma to the mother's birth canal) yet still grow a very large and well-developed brain.
Third, there is no natural tendency to monogamy among mammals that show sexual dimorphism of size if the male is the larger of the two sexes.
So the woman's dilemma is that if she is to have grandchildren, she needs a co-parent and helpmate who will stick around until her offspring are self-sufficient. But men are not inclined to monogamy, so they somehow have to be enticed into staying.
What woman has working to her advantage is that her man can't easily tell whether she is ovulating. For a male mammal, knowing when any particular female is in estrus is important because that time represents both its best opportunity to breed with result and the time when it is most important that the particular female be guarded against breeding attempts from other males.
And in many mammals, distention of the breasts is a visual cue that estrus is either near or in progress.
Taken together, that means it's difficult at best for a man to know when it's safe to leave his woman alone and not risk her next child being some else's. And the distended breasts can be instinctually perceived as a display of always being receptive to breeding.
Under these circumstances, evolution obviously should favor men who instinctually associate distended breasts with readiness to breed because they also are instinctually inclined to stay around, in the process inadvertently becoming a co-parent.
In other words, it is logical that evolution would favor the genes of those who are "boob men."
So, ladies, the next time you catch a man ogling your chest, don't blame him, it's just the Darwin in him talking.