You're missing an important part in what marriage does:
Formal representation for each other, may it be law or health. That means you have someone can make decisions for you if you're not able to (or get information about your where abouts).
If both expect to stay together some time it simplifies a lot of things.
And if it turns out you don't like each other anymore, there is always the option to get divorced.
wouldn't that be mostly an insurance company? The 2 main things that Amazon delivers are fast delivery and hassle free service.
ordered? At your doorstep in a day.
not happy? send it back, no worries
broken after 2 years? Send it back, no worries
I can't see that delivered decentralised without a massive insurance or CoC behind it.
But if: Would be awesome
That's Captain Raynolds Galactica!