What Is the Primary Driver of High Energy Use in Pure PoW?

The high energy use in pure PoW is primarily driven by the continuous, global competition among miners to find the next valid block hash. Miners are incentivized by block rewards to dedicate massive amounts of specialized hardware (ASICs) to constantly guess the nonce.

This competitive guessing game, known as the 'race to the hash', requires constant electricity consumption on a massive scale.