Career women (and men) presumably hit their peak salary earning years in their mid-30's to 40's. And if they haven't done so already, when exactly is the "perfect" time to have children? Women are looking at other options besides giving birth... as in can't someone else do it?
Even if the couple still makes enough income, it would put a huge damper on their career (think of lead Hollywood actresses, not getting parts because of obvious reasons, something men do not have to worry about.) So why should women have to put their life on a one to two year hold?
This is now becoming a "thing" called designer surrogacy. Women are now hiring surrogates - and paying them well - to have their embryo implanted inside another woman who will "incubate" the baby until birth. It has nothing to do with infertility or medical conditions, just pure choice to allow someone else to suffer the burdens of childbearing while still working on a flourishing career, running a marathon, a busy MD or skinny socialite who "doesn't want to get fat."
Labor is being outsourced but paid a fair. tax-free wage - $30,000 to $50,000 per pregnancy plus more if carrying twins or in need of a C-section. Also maternity clothes, support groups, housekeeping, nutrition lessons, babysitting, breast milk compensation and lost wages if bed rest is required are all part of the package, so more like a $100,000 plus deal. That's less than one year's wage.
And the women who give the gift of life feel empowered by providing happiness to a family, regardless of the reasons behind it.