As an example, the reason that coupons (like $1 off a box of Wheaties) or refunds (good for 1 airline ticket) and similar "financial instruments" have expiration dates on them is because it is required by accounting rules. When those items are issued, companies need to put them on their books as liabilities, and having to keep around an ever increasing accumulation of liabilities for many years would give a "wrong" picture of the financial health of the entity, when the purpose of books is to give a "right" picture.
(your take is not more nuanced, it acknowledges this practicality aspect. to extend the newtonian/einsteinian analogy, you're advocating ignoring the ∆x² term as the lim ∆x→0 version of the calculus derivative rather than the approach taken by analysis :)