It simples man, having Mbappe in PSG's squad made them looked like a Mbappe centric, everything and anytime is about Mbappe. Meanwhile the paradigm of PSG's ball totally changed once he left. They're rebuilding back what we called as a club. A team that has team working, chemistry, passion in winning, and collective gameplay. They're not a Mbappe centric anymore. That's the point.
Humans can be jealous. My guess is that some of the players might be angry that the club was given preference to Mbappe. PSG depended so much on him and neglected other players. But his departure brought out the best in other underestimated players.
We are now seeing the best in players like Dembele. There was a report that Luis Enrique motivated Ousmane to convert some of the chances he creates after Mbappe left. And he took the advice and now he is a frontline candidate for the Ballon d'Or. I also think that the players become more united because there are reports that Mbappe was proud and selfish.