Motherhood is a bad deal.

Mothers get all the blame for anything wrong with their kids. If a mother has to raise her kids alone after her husband abandons her (with all the disadvantages that come with being a single bother), she's blamed for not choosing a better partner. If her kids don't act like perfectly behaved automatons in public, she's the one looked down upon for it, If her kids have any adverse childhood experiences outside her control, she is specifically still the one blamed for not protecting them better.

Mothers get all the shame for not living up to unattainable social ideals related to being a mom. It used to be the case that an entire community used to be involved in the raising of a child. Now a lone woman is expected to provide the socialization of a couple dozen people by herself, and is expected to navigate multiple generations worth of contradictory advice without any help. And she's expected to do it while working full-time on top of it.

Mothers get none of the status that parenthood provides. Men are looked up to for convincing a woman to let him cum inside her, and are rewarded with having higher pay on average than they would otherwise. Mothers are treated with contempt if they bring having kids, and get the reward of a markedly reduced earning potential.

And on top of that, mothers are not compensated for the labor of raising their kids in any way. But since the work that goes into raising a kid is impossible to quantify, any attempt to leverage that labor is mocked and dismissed. And even if the woman gets child support, it's generally not enough to cover the costs of raising the kid (and most men don't pay what they owe).

Therefore, since this is the current state of motherhood, it is entirely reasonable that women are choosing to opt out. They don't benefit from it in any way, and get gaslit about supposedly wonderful kids are in the name of reversing the falling birthrates. And since women are increasingly choosing to opt out of motherhood, society is going to have to actually make it worth women's to actually be mothers if they want that to change.