One reason past performance is invalid consideration is?

The reasoning behind why past performance is considered invalid consideration is primarily because it does not involve a new exchange of value. Contract law requires that for consideration to be valid, there must be a new promise or performance that is exchanged between parties. Past performance refers to actions or services that have already been completed prior to the formation of a new contract. Since nothing new is being promised or exchanged at the time of contracting, it fails to meet the requirement of fresh consideration necessary to support a new agreement.

This establishes that the essence of consideration in a contract is the mutual agreement to exchange something of value that has not yet been fulfilled. Therefore, past performance cannot be utilized as a basis for a valid contract consideration in this context.