This issue probably has very little to do with sperm quality or the availability of abortion, but with our culture in general. The assumption that teen pregnancy = bad, the stigma around it, etc. In your comment, the mentality that life starts later. Like, life starts at birth.
I'd imagine that same mentality is responsible for the loneliness epidemic written about in the same places. This idea that life is some achievement to be gained after doing things like going to college. Like, you can't live your life until you've completed some rites of passage, except they get increasingly more detached from reality every decade. And as we read about in the WaPo and other sources, has the college rite of passage really served the amount of people who have gone through it? Student loan debt, bad job prospects, starting life later...
Another interesting fact, younger couples have healthier children. Not like, 13 young, but late teens early 20s young. As couples age, the risk of genetic faults and things like autism rise.
tldr, it's not sperm count or abortion. Our rites of passage into adulthood suck.