The federal government was not created to fulfill such a purpose. It was created and limited to specific delegated powers designed to basically deal with issues external to the U.S. and judicially resolve Constitutional controversies. The Tenth Amendment confirms this purpose that "any power not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
Marriage and the family are simply not among the enumerated powers of Congress and, therefore, not a federal issue. It's a states' issue. Our country was created not for government to fix all our problems, but for government to protect our freedom to fix our own problems.
However, the federal government has made just about every part of your life and mine their business regardless of the Constitution. The income tax for instance has allowed government to invade our private lives that is none of their business. One of those things is if you're married (none of the government's business). Nevertheless, it is now unconstitutionally become their business. Just like all the other stuff, SCOTUS can now rule on a matter that is none of their constitutional business becasue SCOTUS will not declare acts of Congress unconstitutional. (The ability to tax income was from the 16th Amendment not an act of Congress. But implementation has been very unconstitutional becasue it has allowed the federal government powers not given it by the Constitution.)
The purposes of this government are stated right up front.
"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."