Wait, do you know women that stop wearing their engagement ring after they’re married? Every married woman I’ve met (that doesn’t have a hands based labor job) wears the engagement and wedding ring. All the women in my family have them soldered together some time after, so they don’t independently spin on the finger.
I am curious what region you’re from. I would guess it’s outside of the US, but perhaps there’s an area that differs from the norm I’ve experienced.
If you are indeed outside the US, I’m guessing it’s the American tradition of engagement rings, without the tradition of continuing to wear the engagement rings. That truly would be a (bigger) waste of money.