RBC is devoted to carry O2 and CO2 in the body. It needs more space to hold the gase so that other cell organells should not present whithin it. In addition if mitochondria would present it would have consumed all O2 and hence could not transport O2.
As per my concern by: kamala
During the course of evolution, it is designed in such a way that though erythrocytes are carrying so much of oxygen with it, can't utilize it for aerobic respiration (since it lacks mitochondria). Otherwise there would be no proper O2 supply, if it consumes for its needs.
Aerobic respiration uses oxygen and requires mitochondria by: Toby
The idea is quite basic. To respire aerobically, oxygen is used up. Since the major role of red blood cells is to transport oxygen, it would not make much sense for the cells themselves to use the oxygen needed by other cells in the body. In addition, red blood cells would need mitochondria, which takes space (could be about 6µm^3 in volume). To maximize efficiency, mature erythrocytes pretty much empty themselves of mitochondria & nucleus and then fill themselves up with as much hemoglobin as they can.