Because a higher percentage of Americans are working low-wage* jobs than in any other developed country. And it's not even close.
That means that if we leave it to 'the market' to solve this problem, too many women here in the U.S. will have to choose between purchasing contraceptives and paying the bills. It's that simple. They will be unable to afford the relatively small upfront cost of avoiding the much, much more costly event of having a child that they can afford even less. No woman should ever have to be in this position.
And for what it's worth, this is true for married women as well as single women. Because married couples, too, are often stretched to the limit, and have no money left over to pay for contraception. So even if we buy into their abhorrent slut-shaming rhetoric, married women who supposedly have the blessing of the wingnuts for their sexytime are forced into an untenable position by the cost of contraceptives.
You'd think even wingnuts could grasp this logic. Except I'm betting they're perfectly OK with this. While they haven't yet overtly defined genital sex as a luxury good that you should only engage in if you have the time, energy, and above all the money to raise another kid, it's pretty much the direct implication of the positions they've taken in recent months.
It's just a matter of time before they say it in so many words. You can hear them now: "There is a third option: not having sex." Well, yeah. And how do we feel about this? If a couple is perpetually struggling just to pay the rent and keep food on the table, does that mean they no longer have the moral right to have sex?
Yep, that's what they're saying. The sooner they say it out loud, and can be forced to publicly own that belief, the better.
*Defined as earning less than 2/3 of the median hourly wage of one's country.