Unless you are in a city or state which requires insurance companies to cover SRS, they don't have to. ACA says they can't not treat you if they would treat others the same. This means, basically, that if you broke your arm, they have to set it just as they would if you were not trans. It does not mean trans treatment is covered. The hormones are often covered because cispeople also receive hormone treatments and therefore they have to cover them for you, or face lawsuits.