I'd argue it's a symptom of humans holding the past in high respect.. What other animal cares so much about what kind of person they were last year? Regardless, we're wired to pay careful attention to the details of the past by replaying the important details in the back (or front) of our minds. Maybe the memory playing when we see the wedding band reminds us why we're with our partners. Pretty rad tradition if you ask me, even if it means we show our respect to it buy spending a considerable amount of income on it. Or could it be a result of our respect and seeming obsession with income in the first place?