How does pasteurization lead to more diversity?

The variety of mushrooms that we can cultivate varies not just in appearance and flavor, but also in their growth rate and ability to outcompete other microbes. Oysters, our most commonly cultivated mushrooms are so vigorous they can grow on most substrates. Other species, like hen of the woods, are slow-growing and benefit from the leg up pasteurization or sterilization provides. By treating your substrate with either of those techniques, you'll have more success growing a wider variety of mushroom species.