Getting out of a relationship before entering the next one makes sense, right?
But why would anyone marry his/her own self in the first place?

To send a signal? ‘I have removed myself from the (singles) market’?
As a publicity stunt? Proving – unintentionally, that marriage continues to be an important institution, at least at the symbolical level….

On the other hand, why bother? At all…
Specially now, after the advent of the ‘prenuptial arrangement‘….

So, marriage is, in reality, only about ‘property’? Who gets what after the couple separates? ‘Naturally’ or otherwise?
But, again, why make it a special thing? Property had been formally ‘coded’ about the same time as marriage was… why introduce another set of regulations, on top of those pertaining to the ‘mere’ individual property?

There must be something else…

And that something must be in our heads!
‘Property’ has more or less the same meaning all over the world.

Culturally, there are many forms of property ‘out there’ but the most ‘advanced’ cultures ‘use’ the same three main types of property, each in it’s own ‘mix’. Private property, state property, communal property…

Meanwhile, each culture/civilization has it’s own type of marriage. Or used to have, until very recently. Which types of marriage differ widely and in many ways.
From who can enter a marriage – number of people, ethnicity, religion, caste, etc., to how a marriage ends.
From the conditions which must be met before the marriage to the consequences of the act. And to the consequences of the marriage being ended ‘before time’, if possible.
Not to mention the wide gamut of rights and duties each member of a marriage might have, according to local rules and (by)laws.

If you think of it, ‘property’ is almost ‘natural’. It makes a lot of sense, ‘functionally’ speaking, to be precise about which is which. And about which is whose.
Life is a lot simpler when each member of a community knows what/how much can be had/used/eaten without anybody else having any say about the matter, what must be left alone and whose ‘permission’ you must ‘acquire’ before ‘trespassing’.

Meanwhile, ‘marriage’ is a lot more artificial than ‘property’. Leave alone the fact that the rules are far more complicated – and far more diverse.
In practice, marriage has been really important only for the ‘top’ members of any given society…
And the ‘fun’ fact is that the higher the rank of the individuals concerned, the more ‘leeway’ they used to have…

Henry the VIII had ‘invented’ a ‘new religion’ in his attempt to bend ‘the rules’ according to his wishes, the French monarchs had been famous for their mistresses… and a ‘modern’ financier had been recently convicted for ‘lending’ underage members of his ‘harem’ to some of his buddies…

That ‘something’ is, definitely, in our heads!

NB!
I’m not implying that that ‘something’ is good or bad!
We are the ones who attach ‘values’ to things/concepts.
We are the ones who ‘notice’ things and relationships, use them – properly, for a while, and then experiment in ‘abusing’ them.

A (beautiful) woman marrying – and divorcing, her own self is perceived as being a ‘fun thing to read about’ while gay couples becoming able to establish a formal family is perceived, by so many, as being ‘a threat’.