The intensity of the wave become weaker when it spread further away into 2D or 3D space.
If it is a point source and the wave spread into 3D uniformly,
the surface at radius r is , so the intensity decrease as .
Is it easier to understand how the intensity decrease with r this way?
It will be too complicate to draw too many wave together.
I did not know how to present your ideas with the URL you have procided. Sorry! ???