I have a hypothesis regarding the lowering of male fertility.
In the past, obviously, very healthy sperm was a good thing, evolutionarily speaking.
However, since the normalization of abortion, sperm that works on the first go is more likely to not reproduce: the woman gets pregnant with a guy she only just met, gets an abortion, and the abortion often causes them to ultimately split up and be more careful in the meantime. On the other hand, crappy sperm allows a couple to enjoy sex many times before having an "accident", by which point they have bonded sufficiently to be much more likely to keep the foetus.
Inb4 evolution doesn't work that fast.
Maybe, but bear in mind that sperm mobility genes are the fastest evolving genes. And when you are considering things like abortion, the evolutionary pressures are more like farm breeding than slight advantages in the context of life in general.