1. Lack of support network -- many people living as just a couple or alone (and the strain on couple is so high that likely they will be alone soon).
2. Social emphasis on individualism rather than self-sacrifice or community focus.
3. Breakdown of community and trust -- so watching and keeping kids safe is full time job. Must be driven to and from everything, no playing by themselves after school.
4. Increased education -- older parents with more debt and pressure, working in more demanding and/or rewarding jobs.
5. Children need more -- expense of having child keeps increasing. The cost of all goods rising relative to wages, but also the cost of school, daycare, extra-curriculars, etc. Basically having a child is a huge cost, the medical bill just to have the child can be $20K in some hospitals. In most of the world that would mean no one could have a child in a hospital.
6. Changing norms have greatly increased what is expected of a parent raising a child. Ignoring external cost increases, this has profoundly increased the cost and time investment to having a child.
7. Economic changes (e.g. 30 years of wage stagnation) all but force a family with both parents working, meaning parents have to work, and then thanks to #6, also do more at home.
So parents are expected to do far more with far less, with no support from family, community, or society.
This structure has fallen apart in the last 100-150 years or so as wealth, individuality, and other factors you note have dominated western, especially American, life, although the same thing has happened widely in Europe.
Thus the burden, instead of being born by many and therefore not being "so bad", is instead entirely born by 2 or 1 and it is of course that multiple more work. If 25 people would have shared the burden before, you, alone, are now doing all of it, along with the burdens of increased costs, expectations, responsibilities, etc. It's no wonder that raising kids is such a non-starter for many.
The solution, from my point of view, is not to not have kids. That just promotes losing our humanity. For me it is to change those structures that make family so hard.
If we lose what makes us human... wtf is the point of all the things we build.
Now we work 40h+ per week, not including the daily commute, the various appointments, the kids soccer game/karate lessons, helping them with their homework, doing various chores around the house, preparing meals, etc...
We have more comfort, luxury and product selection than ever, but there's a price to pay in terms of energy, time and money.
Until that becomes a rare viewpoint, or at least one with no power, we will have these problems