Power radiated from an antenna propagates outward in a mostly spherical distribution (not accounting for directivity, ducting, etc..) and a sphere has an area of 4 pi r^2. The amount of power received is proportional to the area of the receiving antenna. You will find, if you do the simple math, that r^2 get big real fast and that any practical receiving antenna at any significant distance subtends only a tiny fraction of that sphere's total area and thus only receives a tiny fraction of the radiated power.