In glycolysis, the conversion of glucose to pyruvate results in a net gain of 2ATP molecules. In gluconeogenesis however, the conversion of pyruvate back to glucose requres 6ATP molecules. Why does there seem to be an apparent loss of energy?
This energy is not lost, it is dissipated as heat.
And this must happen because of thermodynamics -- the direction of the reaction is simply determined by the difference of energy between substrates and products, and it must be positive for the reaction to happen spontaneously.