When you're trying to have a baby, and it takes 10 times to get there, it's not that big of an issue. When one mistake ends in pregnancy vs. ten mistakes, it can make a considerable difference.
Just a thought.
It is well known that people don't have the same strong community bonds to those in the same physical space that they used to.
In an environmemt like this sex becomes rarer and riskier as partners are more unknown.
Giving birth and raising children also feels riskier as individuals don't have a community to rely on and absorb the added burden of child rearing.
A 0.2% difference in birthrate makes a massive difference on the timescale of civilization, so it is a very interesting question to me.