That’s the (contested) argument, at least. Mind you, it isn’t just finance academics who like diversification. Within the natural resources sector, a well-established school of thought states that more (mines, oil wells etc) is indeed more.
From geology to politics, unions to prices and the odd operational calamity, reality can render even the most careful resource project assumptions obsolete. If a lot can go wrong, then it is logical for extractors to hedge, via new commodities, jurisdictions, or processes. What’s more, unlike a retail brand or software patent, all resource projects are finite. As the value of a mining asset is depreciated as it is steadily depleted, the urgency to find the next new thing grows.