Why isn't all the gravitational energy going down hill converted into kinetic energy?

Energy is not a physical unit. It is a philosophical concept and an accounting technique used to analyze mechanical and chemical exchanges. In nuclear physics it is defined as a wavelength of light, in biology it is a synonym for metabolism, and in public utilities they say energy when they mean connectivity. Anybody who uses the word in any other context either does not know what he is talking about, or is peddling something you don't need.

You need to study this subject more carefully, avoiding slang terms and cliches. Kinetic energy is an imaginary concept, and gravitational energy does not exist at all.