Why does the AAMVA CDL Manual direct drivers to confirm emergency equipment both is present and works, rather than just checking that it is present?

AAMVA CDL Manual §8.1.3, p.8-8-1

An emergency triangle that won't stand up or a fusee that won't light is effectively the same as having no equipment at all when a real breakdown happens on a highway shoulder. This distinction between presence and function is a common point tested on CDL knowledge exams and a real safety gap in practice.