Why is the chloroplast not called a “power house”?

Maybe because it is not a “power house” (and neither is the mitochondrion): the “power house” in both cases is the sun (fusion reactions, liberating energy in the form of photons (sunlight)). read more

The chloroplast is not called the powerhouse of the cell simply because it does not give energy to the cell per se. Chloroplast are an integral part of energy creation as it allows for cell respiration to occur by creating the glucose through photosynthesis that is then broken down by the mitochondrea into ATP (energy). read more

The mitochondria is called the powerhouse of the cell because it is responsible for producing most of the cell's energy, or adenosine tri-phosphate (ATP). Mitochondria are able to multiply in response to the energy needs of a cell, so that cells requiring more energy to function are powered by more mitochondria than cells with lower energy needs. read more