I don't agree comparing diamonds with crypto. Demand doesn't connect them; diamonds functionality is in the industry, limited and not making it valuable. But the demand in jewelry is fake and it's a matter of marketing (De Beers company exclusively)
But cryptos have valuable functionality, helping transactions, freedom for financial systems etc.
Demand is important, but it's not everything. Cryptos will change the world's financial system, but not every demanded good would.