Why does anaerobic respiration release so much less energy than aerobic?

Because it does not finish the job. Anaerobic respiration breaks glucose part of the way down and stops; aerobic respiration takes it all the way to carbon dioxide and water. The energy left over is still locked in the products.

The two equations

Aerobic, with oxygen available:

glucose + oxygen  ->  carbon dioxide + water  (+ a lot of ATP)

Anaerobic in muscle, without oxygen:

glucose  ->  lactic acid  (+ a little ATP)

Anaerobic in yeast, the version used in brewing and baking:

glucose  ->  ethanol + carbon dioxide  (+ a little ATP)

Look at what is left at the end. Lactic acid and ethanol are both still complex molecules with plenty of chemical energy in their bonds. Carbon dioxide and water are not — there is nothing further to extract. Aerobic respiration releases more energy because it finishes the oxidation.

That is the explanation examiners want, and it is better than "aerobic releases more energy", which just restates the question.

Why muscles use it anyway

If it is so inefficient, why does the body bother? Because it is fast and does not need oxygen delivered.

During hard exercise your heart and lungs cannot supply oxygen to leg muscles quickly enough. Anaerobic respiration keeps ATP coming while that shortfall lasts. It is a worse deal per glucose molecule, but it is available immediately.

The cost arrives afterwards. Lactic acid builds up, causing muscle fatigue, and has to be removed. That requires oxygen, which is why you keep breathing hard after you stop running — the oxygen debt. The lactic acid is carried to the liver and oxidised, and the breathing rate stays high until it is cleared.

What questions actually ask

Rarely "state the differences". Usually something applied:

An athlete's breathing rate after a sprint. The chain is: oxygen could not be supplied fast enough → muscles respired anaerobically → lactic acid accumulated → oxygen is needed to break it down → breathing stays rapid until the debt is repaid. Each arrow is a marking point.

Yeast in a sealed container. Expect carbon dioxide and ethanol, and expect the question to link the gas to bread rising or the ethanol to brewing.

Why plants and animals both respire. A reliable trap. Plants respire all the time, including in daylight while photosynthesising. Respiration is not the opposite of photosynthesis in the sense of only happening at night.