We have made raising children too difficult. It used to be that the first ~5 years required constant involvement, then required less involvement as your child grew older/became more independent. Now you have to be constantly preoccupied with your child for almost two full decades. A few reasons:
Constant supervision: It used to be normal for kids to go to and from school, a friends house, etc on their own. As they got older, it was acceptable to not know where they were up to the point where there were PSAs at 10pm asking "Do you know where your children are?" This is now considered terrible parenting, and may result in CPS getting involved.
Education Management: It used to be that as a parent you were expected to sign off on your child's progress report, which arrived at 1-2 month intervals. Schools now expect parents to check apps, portals, emails, and assignments daily. Beyond what the school requires you to do, parents feel they must stay involved to make sure curriculum, school culture, and influences align with the values they are trying to instill in their children.
Social media/internet: This is a double-edged sword. You don't want your child on social media and all the problems that come with it, but you also don't want to socially ostracize them from all their peers who use that as their primary form of communication outside of school. If you allow it, you have to constantly monitor their activities and have concerns about online bullying, grooming from predators, and algorithmic manipulation.
Lack of Community Support: It used to take a village to raise a child. Now members of the village are afraid to even speak with a child that is not theirs lest they enrage the parent. This imho is the reason that poor people are willing to have more children, as people from poorer socioeconomic backgrounds are more likely to be close to, if not living with, other family members that can help raise the child, while more successful people may not even live in the same state as their parents anymore, much less the rest of their family.
Economic Pressure: With the rising cost of living, many more couples feel the need to have both working full-time in order to make ends meet. Combined with the lack of community support above, many couples who don't feel they can adequately provide for a child elect not to have them.
This post is already too long, but there are many more examples. This leads to people who are anxious about raising a child "properly" electing to have fewer or not having them at all, while people who could give a **** about how they raise their kids continue to have them in abundance.