Unsystematic risk is the diversifiable risk specific to the considered company, e.g. risk resulting from geographic location. Since unsystematic risk is diversifiable risk, the risk can be eliminated by holding a well-balanced portfolio and the total risk is equal just to the level of systematic risk (undiversifiable).
Therefore, investors shall not be compensated for the unsystematic risk in the form of an excess over the risk-free rate of return. They shall only be compensated for the systematic risk.