Yes, there is cubic zirconia and things like that. But notice how society reacts, and rejects cubic zirconia? It isn't because cubic zirconia is inferior. It is because it is not expensive, so it makes for a poor costly signal!
Not gamed in that sense. Gamed in the sense that a diamond ring is purchased not as a show of commitment, but with the intent that it will be perceived as a show of commitment by the receiver.
If the giver knows that the receiver is treating the ring as a sign of commitment, they can decide "well I'm not really committed to this person, but I can help convince them that I am by buying them a diamond ring."
Diamond ring is purchased as a show of both wealth and commitment. The recipient is left to judge- if the giver is very wealthy, it is clearly not a strong sign of commitment. If the giver is very poor, it is clearly a strong sign of commitment.
Because you could buy a suitable ring there (it will have an icky feeling to most people, so it will be cheaper than a "new" ring) and then sell it back when you now longer needed her to think you were committed.
Yes, there is cubic zirconia and things like that. But notice how society reacts, and rejects cubic zirconia? It isn't because cubic zirconia is inferior. It is because it is not expensive, so it makes for a poor costly signal!