Come on. You must know how insurance premiums are set. There is statistical data over many years showing that a certain percentage of female employees, of a certain age range, will use contraceptives for a certain amount of time. That will determine what portion of the premium pays for that benefit. That's what actuarial science does. And the contraceptive mandate isn't unlimited. The benefit can be restricted to prescriptions obtained from in-network providers. And an employer group plan can establish tiers of preferred brands, and require prior authorization for certain products. Contraceptives are subject to the same medical management as other pharmacy benefits.
And BTW, what any health insurance plan covers is set by
state laws. It's been that way since the 1940s. And ACA really didn't change that, with the exception of about a dozen
evidence-based preventive services (one of which is use of contraceptives.) Even before ACA, something like 28 states required all health insurance plans sold within their borders to cover contraceptives. And some (I think TX was one) required no cost sharing. In fact, the ACA mandate was based on what some states already required.
If you have the time and inclination, here's a good article from Kaiser on the birth control benefit.
Private Insurance Coverage of Contraception
And here's a summary of how the preventive services benefits for women were determined. It was the work of the Institute of Medicine (part of the National Academy of Sciences. Which is a private, non-governmental academic organization.) And it was based on the medical literature. Not on political ideology.
https://www.nap.edu/resource/13181/reportbrief.pdf