"Why is the government able to dictate the terms of a contract between two individuals?"

You answered that question yourself. It's a contract. Point: It's easier to bring 12 lawsuits against states challanging equal protection under the constitution than to get heterosexuals to give up their right to a legal marriage. Consider this;
the alternative at the moment to a secular marriage is a religious marriage.

Many countries have government sponsored health care. The fact that the united states does not, that it has a private for profit system and has such a high infant mortality rate, is criminal.