I don't understand why Delta places a time limit on e-credits at all.

Over time, money gets cheaper due to inflation - the flight value of e-credit goes down every year.

A significant portion of customers will never use their accumulated e-credits since life happens: people stop flying and forget about e-credit, and, unfortunately, people die.

Allowing non-expiring e-credits will benefit Delta. Even while they must book all the outstanding credits as liability carried over to another year after year. Accounting process should not impede company profits.