“Driven” suggest more than half of total pregnancies,

Less than 20% of a total is “significant”?

The amount the percentage represents is irrelevant. A billion people could be involved, but if the total is 7 billion, it’s not going to be a significant part of the total trend.

In the terms of your analogy, this is about 3 people out of 20 pedaling a (weirdly long) bike and steered by all of them (somehow). Would you say that group of 3 are driving? Or would you concede it’s the two groups of 6 that are mostly driving the bike?

Your "words wholly" includes more than whatever you think it does.

My point has always been about this study

Has it? I think you're far less clear and careful with your words than you think you are. You've been arguing from the start that less than half of something isn't and can't be significant. We aren't even discussing the text in this study that you can read in the screenshot:

More than half the drop of America's total fertility rate is explained by women under the age of 19 now having next to no children.

What you're saying now about “the traditional driver of USA birth rates” isn't reflected in your other comments.