As you say, a lot of the reasons people give are flippant and superficial. The most common claim I've seen is that everything is too expensive, but this is untrue. For some time, we have been richer than we've ever been in history, on the whole, and yet we witness decline. And all of the money-oriented incentives gov'ts have deployed have also petty much failed.
The problem is composed of multiple factors. However, I would say that there is a unifying element, a master key, that explains all of these elements, and that is consumerism. I mean "consumerism" as an ethos and as a matter of culture.
1. People are creatures of convention. Very few people operate or live life outside of the conventions of their times and of their culture. Culture creates the grain of life most people will follow, for better or for worse. In general, people are terrified of swimming upstream or going against the grain.
2. Subjectively speaking, culture determines conventions, sensibilities, patterns of life, purposes and goals pursued, and what is valued. Culture, whether explicitly or implicitly, imbues people with a sense of how life ought to be lived and where energies ought to be spent. It shapes attitudes toward the facts of life.
3. Inevitably, culture is institutionalized in law. As law is a teacher, culture is partly perpetuated through law.
4. Culture is also replicated and reinforced through media and education. It is usually insinuated.
5. Consumerism construes human nature and human fulfillment in terms of consumption. The obvious case is economic consumption. We believe buying things will make us whole. We believe money is the root of happiness. The life is the market and the market is life. Everything is for sale, for the right price.
6. This already creates an opposition. If consumption makes us whole, then children are antithetical to wholeness. After all, children are consumers! They are competitors. Given the choice between a new luxury car and another child, many couples would choose the car. People routinely make this calculation. They will limit their brood, because children eat into budgets and into time that could otherwise be spent on luxury items and vacations on tropical islands (mutatis mutandis).
7. If consumption makes us whole, then everything else that might be desired is recast as a matter of consumption as well. Even human relationships are reconsidered in consumerist terms. Sexual relationships become consumerist and transactional. Sex itself becomes commoditized, and becomes an instrument of the market. Beauty is desecrated and exploited to push products and services. A functional prostitution and an exploitative stance invade and pollute relations between the sexes, rendering them totally dysfunctional.
8. Contraception enters the picture. Contraception is the paradigmatic expression and cornerstone of all sexual consumerism. It is the incarnation of sterility and physical manifestation of a "NO" to life. It is a manifest contradiction of the essential and core function of sexual intercourse, which is procreative (the other end, the unitive, presupposes the procreative purpose, and so the denial of the procreative is a denial of the unitive). Its acceptance and normalization dethrones the procreative and elevates the pleasurable in its place. Thus, sex is no longer pleasurable. Sex is now for pleasure. The paradox, of course, is that doing this destroys the pleasure of sex, producing a pathological hunt for pleasure that is increasingly bizarre.
9, By denying the procreative, we undermine the significance of the deep complementarity of the sexes. This destroys sexual normativity and opens the door to a consuming and obsessive pursuit of an increasingly unhinged and dizzying array of erotic perversion. Children again become opposition. A child is a wet blanket thrown on the hot fire of deviant eroticism. This way enters abortion as a solution, and the pursuit of intrinsically sterile sexual gratification.
9. Consumerism propels careerism. The career is underpinned by the presupposition that you will need money to consume. A career is your path to making more money so that you can be more happy. Universities are reconfigured away from fuddy-duddy old school liberal arts education to job training centers. Woman are now taught that to be a fulfilled woman is to seek a career. Marriage and childbearing are postponed, not only to attend university, but to spend one's most fertile years shoring up one's careers after graduation. One must justify that expensive education (expensive in time and money). Careerism sacrifices the family for the mirage of consumerism.
10. Now, human life is also commoditized. When women do come around to wanting children, whether for good or bad reasons, they often discover that they are too old, having made a sacrificial offering of their fertility to their corporate god. But we believe we are entitled to children. We believe we are entitled to other human beings as instruments of our fulfillment. So we pursue fertility treatments like IVF. IVF is consumerism on steroids.
12. Consumerism reshapes social practices and life patterns. It created friction and impediments that make having children more difficult, because the assumptions that underpin it maintain that you won't have children, at least not until later. The implicit support, the social and economic architecture of the world and its operations and customs, become hostile to family life. Bad habits, like living beyond one's means, are fed. We demand a standard of living we cannot afford, and view children as hostile elements that rob us of our birthright.
13. A culture must justify itself. Thus, each failed generation rationalizes its bad decisions to soothe its own collective ego by re-presenting its failures as normative to the next.
The solution really is simple: women ought to marry in their mid-20s on average and start having children immediately. The obstacles are cultural and habitual. Our culture creates friction and our cultural programming causes us to deviate from the successful pattern. Instead of ordering the patterns of human life around human nature and human development, we strap human beings into a Procrustean culture, torturing and deforming them to suit weird and arbitrary standards. Instead of conforming our desires to reality, we deform reality in an attempt to conform it to our desires.
This is human arrogance and human folly.