I can't work in a place where I am working hard and get paid half what the others receiving.. It is unfair.
If we take it from another perspective, AFAIK Mane is doing many charity actions in his native village, not sure how accurate that was but to say that he isn't "hungry" about the money.
I think money always plays a role in the world of professional soccer. I would guess that even if Mane would not care about money at all then his agents and other people would probably still make sure that he gets a salary as high as possible because they also get a share of that sum. The only "big" player that i know has no agent is Joshua Kimmich since a year or so.
That being said i think the main reason for Mane to leave Liverpool was the fact that he was always seen as the second most important player behind Mohamed Salah. I think Mane just wants to be appreciated more. Let's see if he gets that appreciation in Munich.