This is the entire point of most PoW mechanisms. It's a way of "proving" that an miner expended a certain amount of effort or energy to validate a transaction. It also requires that expenditure to be significant enough that gaming the system is expensive. As a result most of of them scale as the effort inevitably get's easier thus ensuring that the energy required to validate a transaction will only ever be capable of growing not shrinking. If it is allowed to shrink the consensus properties start to fail. Whether you think this is a worthy use of that energy will depend on how much benefit you think the consensus properties of your particular PoW implementation are providing.