Klopp has both a job and a reputation to maintain.
The job is to assemble a team to compete at the very top end of the game and win trophies.
His reputation is to have players who believe in him and commit all their energy in a high tempo playing style that wins games.
Both those things will be compromised when you start playing 2 to 3 games every week.
He wouldn't be doing his job as a manager if he didn't flag things that were going to have a negative impact on his staff
and affect his success in the job he's doing and his reputation.
The fact that football players are paid way more than regular jobs and Liverpool players are paid at the higher end of football players is a completely separate topic.
They're paid to do a certain thing and that thing not being as tiring as a Nurse's job yet way more highly paid is, however unfair it may be, irrelevant to the matter at hand.
I would prefer that footballers were playing at the best of their abilities as often as possible and also that the bigger clubs didn't wind up acquiring a huge amount of the best players which they rotate - I'd prefer to see them more evenly distributed rather than players like Mahrez - who would walk into a number of teams - sitting on the bench half the time.