I'm not sure what you mean by "less likely to lose its value over time". If you buy a natural diamond in retail it lost more than half its value the moment you bought it. (it was never worth the retail price to begin with) As an investment, it's a terrible idea.
I'm not saying it's a good investment, to be clear I know absolutely nothing about diamonds. I was just sharing a potential reason why people may favor natural ones over manufactured ones. If the process to make synthesized diamonds becomes cheaper faster than a natural diamond lose its value, then you might be better off with the natural one if you consider it strictly from an investment point of view. Losing 50% of its value after purchase may be better than losing an potentially more after a few years once the industry figured out a way to manufacture diamonds at a way lower cost.
