This is because if the two metabolic processes were to be active at at the same time;
Two molecules of ATPs and Guanosine triphophate (sometimes used for energy transport) will be expended per each cycle, with no compensatory rate of replacements present at the moment in the cell,this affects cell metabolism for energy availability
2 Both Glycolysis and Gluconeogensis are both exergonic processes in cells. The heat energy liberated from these Calorinogenic effects will be higher than what the natural thermodynamic barrier of cells can withstand. Consequently; the heat will raise temperature of the cells affecting metabolic activities of hormones and enzymes which are (proteins) ,and easily denature by high temperatures.
However, in muscles cells,gluconeogeneis is a compensasory process of Glycolysis. This because during active exercise with high metabolic demand in muscles cells, glucose is rapidly metabolise to to pyruvate,(but not at the rate that the Citric acid cycle can metabolise) for Lactic acid production by muscles cells for energy production. Pyruvate must be broken down rapidly so that NAD+ will be available for Glycolysis to continue. Therefore to sustain Glycolysis at this rate continuous supply of glucose is supplied from Gluconeogenesis.
