Why does a rubber ball squeeze harder than an eraser?

The eraser is much tougher in the first place. Secondly, also because it is not hollow like a ball. But the ball is hollow and there is air inside. The ball can be squeezed with this air inside, but only if a hole appears in the ball. If the ball is new and clogged with air to the point of failure, it will not be possible to compress it very much either, since the air will resist. And, since rubber is still a rather elastic material, and even thick, then it cannot stretch. This air that has scored the ball inside will be too much and it will not allow the rubber to shrink inward. That’s it.