Why is the government involved in marriage?

I have several good friends who have adopted or been adopted.  Some of those adoptions have been within extended family.  One was a bit unique.  He was raised by an Aunt and Uncle as if he were their own but there was never a formal adoption until he was going into the Military.   He only ever new his aunt and uncle as mom and dad and he wanted to make sure that his military survivor benefits would go to them.

Of course I don't know all the details but it has caused me to wonder Why did it have to be his legal parent?  Why could he not put her name down?  Perhaps this was a control that was put in place to prevent Fagans from preying on the vulnerable and then signing them in the military in hopes of collecting?

That led me to further wonder why the government is involved with marriage.  I think the reasons are fairly obvious. The society and individuals in it, generally benefit when children are reared in a home where mother and father provide stable environment and moral teaching.   It's been many years since I read The Lord of the Flies but I recall it being a very stark example of the opposite.

I have not read the entire opinions in the recent Supreme Court decision.  But the excerpts that I have seen from the 5 judge opinion and the resulting celebrations seemed to focus on the idea that Love has somehow triumphed.  That frankly surprises me.  How in the world can anyone think that the government can or should have anything to do with legalizing love?  Who can even agree on a definition of what love is?    My reading of the Constitution of the United States is pretty clearly absent of any reference to love, marriage, or sex.  Some will say that is included in the phrase "life, liberty & pursuit of happiness."  However, that phrase is NOT in the constitution, but rather the Declaration of Independence.  What does show up in the constitution is that the purpose of it is the protect "Blessings of Liberty to ourselves and our Posterity"

Some were worried that the unalienable God given rights were not adequately protected in the Constitution and so the Bill of Rights, the original 10 amendments to the constitution were created and ratified.  This with no mention of happiness, love, marriage or sex (except where the word sex means gender).  No, not all rights were specifically spelled out.  Some had to be added later.  But I think that is exactly my point.  Those rights, or rather the protection of those rights, were added.  And until they were added (sometimes late) they were reserved to the States.