Because by limiting access to those resources, they can't be used in ways you wouldn't expect.
Sure, you might invest in cancer research. But did you back the right horse? Soon enough? What about the person who would have engineered earlier detection if they had gone to grad school, but the resources that could have been used to provide that are tied up in your net worth?
No concentrated approach will ever have the same results as letting millions of extra people work on their millions of ideas. The chances of someone hitting on something that sticks increase dramatically with the number of people throwing shit against the wall.
But it can be removed as a possibility by circumstance, which is what this comic is getting at.