Lots of women have realised that they have other options than being house wives and raising children. Many are now pursuing careers, alternative lifestyles, personal interests and hobbies etc. Some simply prioritise their lifestyle over being self sacrificing to others. Having children is not fashionable enviable or considered a particularly high achievement.
On top of this add in all the disadvantages of having children. Career stagnation or gaps, less free time, much much less disposable income. Emotional and energy drain as well as enormous responsibility. Being tired all the time.
If you want children you also need to find a suitable man who you believe (at least for long enough to conceive) isn't a total waste of space. You then risk being tied to this man for life, regardless of his behaviour. Dating has become harder and people are less likely to marry off young and settle down. It is also higher risk as men are now more likely to leave a marriage or relationship than ever before, meaning that a potential mother could be left raising a child or children alone. Men are under less social obligation to provide or offer a traditional set up where the man is the breadwinner and the woman can focus on raising children. This means most mothers have to work as well, which is exhausting, adds costs like childcare and is a good reason to limit the number of children, so then we see women who would have liked 3 children stopping at 1.
Men are more reluctant to have children in general, meaning that finding not only a suitable solvent man is harder but one who actually wants children or is open to it. Many men value their freedom over raising children and this is a perfectly acceptable stance. Sometimes men are fence sitters and can waste time, meaning that women miss the opportunity to have children by spending their fertile years with the wrong man.
There is enormous social pressure not have children unless it's the right time, eg you have bought a house, have a steady job, have the right kind of support network and partner. Women are more judged than ever by the standard of which they raise their children as well as how they parent meaning that it is a social minefield, with the outspoken, the majority and the vocal minority all telling mothers conflicting advice and how they should or shouldn't do things. People are judged on their children's behaviour. People are judged for not going the extra mile and providing constant activities, clubs and opportunities.
Add to this global instability like current disastrous economic predictions, housing crisis, global issues like war and climate change, lack of job security, the quickly changing industries of tech now that ai will eventually be able to replace most tech jobs, and it paints a bleak picture to bring another person into.
Overall I actually myself can't see a single advantage to having a child. I understand for some people it's instinctual but logically speaking it's a precarious decision to say the least.