when ur a plant in a hot, dry environment where water is costly and accidentally using O2 instead of CO2 in one of ur metabolic processes (photorespiration) would mean wasting precious water molecules u could use to process CO2 into the starches and sugars u need to live
when ur a plant in a VERY hot and dry environment where survival is more important than rapid growth and you need to conserve water by any means possible even if it means taking an extremely inefficient, convoluted route towards producing vital sugars and starches
