It was that way in the US for a very long time. Sometime in the last couple decades a new trend arose to wear both the engagement ring and a wedding band together. The logic being you spent 4-5 figures on beautiful jewelry, so it's silly to only wear it during the engagement. (Whether it's silly to spend that much in the first place is another argument.) I don't know if they are in fashion currently, but many jewelers began selling engagement rings with a paired wedding band that is designed to match perfectly and be fused with the engagement ring after the wedding.