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Why does removing additional energy become harder as a system approaches absolute zero?

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Engraved portrait of Rudolf Julius Emanuel Clausius, a bearded man in formal attire with sideburns, facing forward. — thermodynamics Rudolf Clausius (1822 - 1888) is considered one of the central founders of the science of thermodynamics.

As a system approaches absolute zero, the further extraction of energy becomes increasingly difficult due to the principles established by the third law of thermodynamics.

This law states that the entropy of an isolated system approaches a constant value as its temperature nears absolute zero. In practical terms, this theorem implies the fundamental impossibility of ever reaching absolute zero, as the process of removing heat energy becomes progressively more difficult the closer the system gets to that limit.1

While molecular motion does not cease entirely at absolute zero—as particles continue to vibrate with zero-point energy—no heat energy remains available for transfer to other systems. Because entropy is a measure of thermal energy per unit temperature that is unavailable for doing useful work, the diminishing temperature effectively limits the ability to extract further energy from the system.234