Diamonds are made out of carbon, which is incredibly abundant on earth. There's no comparable way to manufacture helium out of anything that doesn't already contain helium; you need nuclear reactions, which are much more difficult to do at large scale.
Helium is made up of electrons, which is also incredibly abundant on earth. Either way, sarcasm aside, I guess you didn't really understand what I was trying to say if you're taking my diamond comparison as perfectly analogous, and then shooting down the idea because it doesn't extrapolate the same way you expect it to.
Up until some point, it was also difficult to manufacture synthetic diamonds at large scale. When the price of the thing desired is right / high enough, technology will be found and whatever costs necessary will become feasible.
