It's all geometry and physics; fulcrums and leavers. Like half the people at the gym, you aren't stressing the muscle enough to really build mass. The factor I'm talking about is sustaining anaerobic respiration. Getting that last rep in on the bench press where you fail and have to use the "oh s-it" hocks and then feel like you're going to barf is how to get big muscles. Doing 1 set of 3 reps like most people at a gym wandering aimlessly or at a warehouse you just maintain a general functioning. Better than fat people at desks slowly dying but far from Arnold.
This reminds me of a moment in a PBS event where they sent modern people to really live like pioneers did. All metrics and aesthetics at the end were closer to that of Army records of the time, in most cases very very far from where they started. "Dudes doing stuff" is an aesthetic like "dad bod" or "yoga girl." The sad part is, most dudes, dads, and girls don't do much at all.
Lumberjacks aren't that fit, office block bros are that fat.