I look at this a little differently. We are not less charitable, we are slightly less aware of all of the many ways we can contribute goodness to the world. If you only consider money, perhaps you are correct since less and less of it is controlled by a greater number of our population.
However, there are no less of us. If we use our imagination and the natural given gifts we all possess in some measure, we can accomplish anything. Example: What would happen if each human in our country were able to send a glass of water to a region desperate for it? 300 million glasses of water would nourish much, would it not? Or, if we sent one idea per person, wouldn't it be possible that one of those ideas could change the face of humanity? Of course!
Peace be with you!