Frankly, diamond rings are not practical gifts. Guys buy a diamond ring to propose to their GF simply because it's customary to do so.
Like many guys, I bought an expensive diamond ring to propose to my wife. To make absolutely sure that she likes it, I brought her shopping to choose the "perfect" diamond ring. My wife wore the ring in our first month of marriage, but subsequently locked it in a safe and never takes it out to look at it. I haven't seen her wear that diamond ring for over 11 years.
After the birth of our first kid, I bought my wife an expensive diamond watch that she chose herself. To this day, she wears that diamond watch frequently to work or outings. I asked her why she wears the watch but not the ring, she tells me the watch is more practical to wear.
Wonder why Sinkie guys can't propose to their GFs with a diamond watch instead of diamond ring, its a much more practical gift and also more expensive.