Yes, my arguments can apply to relationships, but they especially apply to marriage as the contract, both socially and legally, implies set of expectations. When those roles have been removed, why go through all the trouble? Relationships can still make sense in the face of role-obsolescence as people who don't need each other can still "Netflix n' chill." People can even cohabitate and serve no other purpose to each other besides non-platonic companionship. So at that point, why potentially ruin an already good thing?
> effectively nobody is having weddings beyond their means, or feeling required by society to do so
Our experiences differ significantly in that area. Even when it's within their means, it takes them a considerable amount of work to get there. For many, the outcome isn't worth the amount of effort.
Society isn't requiring people to get married, but that doesn't mean that people aren't subject to cultural expectations and peer pressure. As a perpetually single person, I am regularly asked by people whether I've "met that special woman yet." A person who gives more shits than I do would likely feel that they really ought to find that other person and "settle down", if you will. Society doesn't need requirements for people to do things in order to conform.
> There are just some really rich people (or averagely-rich people with really rich extended families) who pay to have fancy weddings because they can.
That, I never denied.