Given that 'marriage' nowadays has nothing to do with family formation, it makes sense for the State to get out of that business.
Or just look at it the other (and IMO more correct) way around: It's actually family formation that is "marriage".
This truth used to be recognised by governments too, as witnessed by the ancient legal term "common law marriage".
If it's time for anyone to "get out of that business", it's everyone but the state.
Given that 'marriage' nowadays has nothing to do with family formation, it makes sense for the State to get out of that business.