The purpose of the ACA is to make healthcare available to more people for the purpose of improving health. Pregnancy, healthy kids, are, as I'm sure you'll agree, a big part of "healthcare" for women. So is family planning, which improves the odds mothers are ready to have and adequately care for children. In other cases preventing pregnancy is a medical necessity because pregnancy risks death for some women. Other women take contraceptives for reasons other than pregnancy prevention and the drugs have a direct effect on health like all other prescription drugs. For all these reasons, the medical community recommends contraceptives as part of a comprehensive health insurance package, along with other services like checkups and wellness visits.
BTW, you saying the government has no responsibility (technically true as an opinion, one of many I guess) doesn't mean much, because it's a goal, reducing unwanted pregnancies, that is shared by people across the political spectrum, many of whom believe government at all levels SHOULD play a role. If you disagree, we should just ignore the number of abortions and babies born to teen mothers, etc. that's GREAT! I disagree as do most people I'd imagine.