I don’t buy that having children is the only really rewarding thing you could do as a human.

Like the only reasons you can come up with is mystery chemicals or soyboys - seriously?

I think it’s vastly more complex than “insert my favourite political reason” and includes many different factors.

Personally I think it’s telling that only the Orthodox Jews don’t seem to have that problem - with an extremely rigid, strict and misogynistic religion as their primary purpose.

Personally as a male I don’t mind having kids but if I were a woman no way in hell would I have one.

In surveys, Orthodox Jewish women rate their happiness with life higher than secular women. You could argue that this is subjective, but I think you would find the same if you look at other derived markers, like substance abuse, suicide, etc.

There can be multiple reasons why modern societies have less kids, but the main theme of Orthodoxy is to keep as much as possible the same as in previous generations. So they would be avoiding almost all the possible reasons given for the decline.