The thing is earning income by doing what it does. If the brownies baked themselves, or the DVDs wrote themselves, I would agree.
Mining is not magic, it takes time, effort, and management. It's easier to bake brownies.
In my experience, the best opportunities are discounted well ahead of the 'fundamentals'.
In mine, so are the worst ;). And that's the rub because investing is a risk averse, avoid capital losses and drawdowns, type of business. It rewards discipline and loss aversion in the long run.