I don’t think that’s it.
Women have been putting off marriage & having kids for one for career & education. By the time they get serious about marriage & family the ideal time to have kids has passed. I think that many assume they can have it all & have kids after 35, but when that time comes, they realize only too late that their time has passed.
Women have adopted the use of contraception to delay onset of pregnancy, but in so doing, sometimes they mess with their fertility.
Women have undergone abortions in the US, & that, too, can affect fertility, along with any sexually transmitted diseases.