If you imagine balls of different sizes but with the same mass on cellophane, and look at the shape of cellophane, then you'll see that smaller balls will make

If you imagine balls of different sizes but with the same mass on cellophane, and look at the shape of cellophane, then you'll see that smaller balls will make cellophane more pointed. If instead of a ball you take a point mass, then the depression will converge into a sharp point. Light can climb out from some depressions but there is a limit on a steepness it can overcome. This analogy probably is not very good for this kind of things, but it shows the idea.