Yes I’m sure part of the reason is women not wanting children, at least at younger ages, due to establishing careers.
And people often say you can delay having children till the mid to late 30 age range. Which is true to a point, but, many women have trouble conceiving the older they get.
The fact is, ease of conception or abilities in that area of life, decline in both men and women with age.
The one thing nobody thinks about in delaying Child Birth is being Grandparents.
If you have a kid at 25 and your kid has a kid at 25 you are a grandparent at 50. Still young and have energy enough to be in a big part of your grandkid's lives (and have fun!). You will also likely live to be a Great-Grandparent.
If 35 & 35 then you are a grandparent at 70, you are old. While you can still enjoy you grandkids when they are little, you likely won't be alive and/or functioning in their teens & early 20's