The fallacy is assuming there’s a “main driving force.” Everyone has their own reason.
So, I can’t speak for anyone else, but for my wife and I, we always planned on having one biological child and adopting another. When we discovered that first step was going to be difficult, we wanted to know why, was there anything wrong with either or both of us? Why were our bodies preventing us from doing what we wanted? So, we set out to try to discover the reason and solve that problem.
I, for one, don’t like anyone telling me what I can and can’t do, even if that person is my own fucking body.
And we did eventually start the steps toward adoption, but that’s another story.