They didn't make it up, they just made a display of wealth (and therefore social status) associated with their product. Brands do that all the time but the signal has always existed.
The advertising serves to put the association between the product and wealth into the common knowledge - https://en.wikipedia.org/wiki/Common_knowledge_(logic). Or in other words, everybody knows that everybody knows that rings are expensive.
> Social signals that cost significant resources for something worthless are stupid.
No, you just don't understand social signals, which was my point. The "costing significant resources" part is the whole idea. Wedding rings and fresh kicks aren't expensive because they're valuable, they're valuable because they're expensive. If you want to understand the idea, check out https://en.wikipedia.org/wiki/Signalling_theory#Honest_signa.... It makes perfect sense (ie, it's rational).
It's equivalent to saying, "I am willing to burn all of this valuable money to prove that I value you".
If we only bought things that were of purely-material value, we'd stop at food, weather-protective but un-aesthetic clothing, and basic shelter. Everything beyond those is social (or hyperreal).