From communication prospective why can't higher frequency ranges be reflected from atmospheric layers and what is the effect of parameters (like temperature, pressure, etc) of the atmospheric layer on reflection of waves for sky wave and space wave propagation.
Different materials reflect, absorb, and scatter different wavelengths of light. The ionized layer at the edge of earth's atmosphere happens to reflect a certain range of wavelength while transmitting others. This is due to the physics of the material.
The reason you can't use the atmosphere to reflect shorter wavelengths for the purposes of communication, is because the atmosphere doesn't reflect those wavelengths in the first place.
The primary parameters affecting the atmosphere's reflectivity is the amount of ionization and the depth of the ionized layer. That largely depends on solar activity. There is a significant difference in this layer between night and day. It is also subject to individual solar phenomena, like flares or coronal mass ejections.