Having a diamond wedding ring is like having a turkey for thanksgiving. That's just the way it's done. It's a part of the culture, maybe you could even say there are religious elements to it.
And that was achieved through marketing.
To elaborate: The "tradition" of diamond engagement rings only dates back to the 1930s, invented almost whole cloth by the DeBeers cartel to sell diamonds. For that reason, I think saying it's a "part of the culture" overstates things. This is not a long tradition that connects us to our ancestors.
2. Keeping mental tabs on which mate always ducks out before they buy the round and making up for it at a BBQ by grabbing a beer out of their Esky. Possibly leading to a fist fight at around 11:30PM and then making up at around 12:01AM.
3. "Sorry mate" as the default response when you're unable to grab the door for a stranger because you're a few CMs too far away.
Not working animal skins? You could if you wanted to.
Well, you’re half right. Baby showers in various forms definitely are in many cultures ancient traditions. Gender reveal parties (at least pre-natal ones; there's some post-natal traditions that have some similarity), quite obviously, not.
A lot of Western culture that goes back hundreds of years has its roots in either religion or the Enlightenment. Holidays, the scientific method, the individualist concept of humanism, capitalism.
Last names. The seven-day week. Learning European history in elementary school. The food you eat every day. Just a bunch of random stuff, really. Think of every way your culture differs from China or Cameroon.
Just cuz you yourself are making the purchase once doesn't mean it is in a thing much of the time.
My wife is a practical, pragmatic person. But she wanted a diamond ring. She felt sheepish about wanting one.
The expense wasn't the appeal, and she's never been interested in signaling consumer goods otherwise like clothes, purses, fashion, jewelry, cars etc. If I had gotten a rarer, more expensive stone that was not a diamond, she would not have liked it as much. The cultural element of the diamond ring was a big part of the appeal.
I'd love to see the market change, to support more diversity in what's normative. But it is too late for us. My wife loves her ring but it was kind of a surprising reaction for her to deal with. She's said that if it were any other jewelry she'd be fine with something other than diamond. She also in retrospect wishes she had been accepting of moissanite. But it was what it was.