What "contractually belongs to them" is exactly what they agreed to work for when they were hired. If that included health benefits exclusive of any particular medication, that used to be a consideration between them and their employer. You may think it better to live in a place where the terms of those contracts are stipulated by the government.
The reason for the U.S. having enumerated powers where states could pass such laws but the federal government couldn't was that if you disagreed with your state's world-view, you could leave that state for one more aligned with your beliefs.
Your premise is incorrect. If the employer were to replace the employees health insurance with a product costing 50% less, the employees would not necessarily receive the former cost of the insurance as new compensation.
There may be specific individuals contracted with Hobby Lobby, but the general "employee" doesn't have any such contract.
