Under that hypothesis, the salary is there to take physical needs as a motivator off the table. If an employee has to worry about physical needs, there's no room at all for any other concern.
Once the salary is sufficient to no longer be a point of worry (will I afford my mortgage, can I support my spouse, etc) only then will additional money serve as extrinsic motivation.
(Which of course spells disaster for things like performance bonuses, which (a) are impossible to target at the right people (see Deming for more on that) and (b) literally designed to stop coming, reducing motivation overall.)
But your salary doesn’t change if you work hard or slack. It’s not a reward for performance.
Similar to how you’d die without breathing but you don’t feel rewarded for every breath. You wouldn’t breathe more than someone else to get more alive.
Maybe not in an immediate sense, but working hard ostensibly makes it more likely to get promoted to a position with a higher salary, while slacking ostensibly makes it more likely to get demoted or fired.
Of course, I say "ostensibly" because the real world doesn't really work like that, with hard workers getting shafted and lazy pricks schmoozing and politicking their way into the very positions those hard workers should've gotten. It'd be disheartening, but it happens to be a decent treatment for my impostor syndrome: everyone else is an impostor, too, so might as well just play along.