The book "Is There Anything Good About Men?" By Roy Baumeister is a non-fiction, readable account of his psychological research, which I think will answer your question and provide many other insights.
Essentially, due to the biology of reproduction, males in most species (including ours) have always had to compete with each other for the chance to reproduce, but females almost never have to compete for just the chance. 95% of females reproduce, versus 50% of men (so some men have more reproductive partners than women do).
In such competition among humans, once we advance to the point that women have a choice in their mates, the men must vie for the women's attention, and men pay to prove to the woman they are worthy providers with resources.
Before that point in civilization, men typically had to prove to the man controlling the women they had the resources to support her and a family.
Women do not compete with each other to see which ones of them get to reproduce; instead that is usually a given, they will reproduce if they want that (and often even if they don't), so their competition has been for the best providers; the best warrior, best genes, best provider, most financial resources.
This dynamic is still in our psychology, only slightly changed by modern society and free women. Men still compete to be chosen and free women still feel they can choose from multiple suitors. And when they were not free to choose (as is true in most societies just a few centuries ago), their "guardian" still chose for them the best (in some sense, depending on the times and culture) of multiple suitors.
The answer is, this is a one-sided competition and men are expendable; as Baumeister shows in his book. The next generation can be produced without most of them; by the best of men fathering children with multiple mothers. Men (and males in most species) play on a very tilted playing field and are at a severe disadvantage in reproduction; it is part of their edge to provide more than just a sexual partner, but also be a provider and defender and therefore preferred by a woman over other males.
Clarification and slight Correction:
From the "Is There Anything Good About Men", p63: The author asks the question, "What percentage of your ancestors were women?"
Yes, each baby has one mother and one father, so each baby's parents were 50% male. But some of those parents had multiple children, and not necessarily always with the same partner. Every baby's parents are 50% male, but you cannot extrapolate from that to conclude that today's human population has an ancestry that is 50% male.
The correct answer has recently begun to emerge from DNA studies, notably those by Jason Wilder and his colleagues. they concluded that among the ancestors of today's human population, women outnumbered men about two to one.
Two to one!
In percentage terms, then, humanity's ancestors were about 67% female and 33% male.
[snip ... illustration ... if a man marries two women, and has a child by each, the combined ancestry of those two children is one male, two women: 33% to 67%) ... end of snip]
Most people are surprised to hear that humankind today had twice as many female ancestors as male ones, because they thought it would be closer to 50:50. When experts hear about this, they are surprised too, but for the opposite reason: They thought the imbalance would be even more severe. That is, they thought it would be maybe 75% to 85% female. Probably it was more severe through much of history, and especially prehistory. In many animal species, close to 90% of the females but only 20% of the males reproduce. The way the human population has ballooned in recent centuries means that most people who ever lived are either alive today or were alive recently, and in modern times the rule of monogamy has spread over large parts of the globe. In past eras, when polygamy (one husband, multiple wives) was the norm, the reproductive imbalance would have been even more severe, Hence whatever conclusions we draw about the differences between mend and women based on the two-to-one ancestor difference are probably understatements. If we had done this research even just a few centuries ago, the ratio might have been three female ancestors to every male one, or four to one.
What does it mean that we are descended from twice as many women as men? It can be explained like this. Of all the people who ever reached adulthood, maybe 80% of the women but only 40% of the men reproduced. Or perhaps the numbers were 60% versus 30%. But one way or another, a woman's odds of having a line of descendants down to the present day were double those of a man.
Also, crucially, the majority outcome is different -- The most common outcome of normal life. Most women who ever lived to adulthood probably had at least one baby and in fact have a descendant alive today. Most men did not.
[bolded emphasis mine, italicized emphasis in the original.]
It is the ratio that matters, 2:1, so 40% versus 80%, or 45% versus 90%, is all the same. The argument being made is simple: Men must compete much harder for a mate than women have ever had to compete, and this is reflected STILL in our psychology, our cultural norms and our individual and collective attitudes. For example, in the US Military, only 7.6% of Marines are women, and 20 of the 336 jobs in the Marines are closed to women. The women could join but do not. Most people still think of battle as a man's job, that men take such risks and women should not. The culture and attitude traces back to the simple biological facts of reproduction, and the disparity of how many children a man can possibly father versus how many children a woman can possibly bear.
The upshot is that men must nearly always compete with each other to find sex, and to reproduce. While women, nearly always, do not have to compete with either men or women to find sex and reproduce. In a modern free society, nearly all women could have sex for free whenever they wish with any of several partners, and reproduce whenever they wish. But only a very tiny percentage of men could do the same: Other than a few glib exceptions, such men are entertainment or sports celebrities, the wealthy or powerful: In short, those that seem to have "won" the social competition to become the elites of society.
Men pay for first dates, and most dates, because they are (subconsciously perhaps) competing for their date's attention against other possible suitors (whether they truly exist or not). When other men are present in a group that contains women, men may compete to pay the tab or bill check to subconsciously prove they are the better-off of the men, the most generous, the one with the most resources to ostentatiously expend (even if they are not). Men tip well, more often, and more money, likely for the same reason: To impress.
The idea that (nearly always) men must compete to reproduce and women do not have to, is backed by Baumeister (and others) in scientific studies, by anthropology, by genetics and by history, which all support common sense observations.
