He wasn't saying good mornings work your traps, he was asking about them separately as their own entities.
Yeah, shrugs are good, but you don't have to only do shrugs. Some barbell upright rows will also hit the traps, and your upper traps are the stabilizers. Same thing with dumbell lateral raises, your upper traps are gonna be the stabilizers.
Good mornings work the lower back, the spine, and also hit your hams and glutes a bit too, heres a link