That’s because they have pretty much gotten away with this up till now. Most other female-oriented health services (pap smears, mammograms, etc.) are now “free” to the patient because when insurance companies resisted they were demonized, set upon and rolled.
Why would they think it could not work again?
Boehner has weeped and given up on every other pledge the GOP has made, so the Democrat women are making a good bet here.