Well I think initially, Mbappe wasn't there for the money, he was there to play football and win trophies. The thing is, as humans when you get to an environment and you're the main man after working your way to be in that position, there will come a time when you earn certain privileges and thus when you see other people of your calibre coming in, you start seeing them as threats. Yes, initially Neymar left Barcelona because he wasn't given the due praises he deserved even in games where he made things happen. I could remember that comeback against PSG in 2017 I think, were Barca won 6 - 1. Neymar was the main player behind the successful comeback but that the end Messi received all the praises and I think that was what also angered him to wanting to leave Barcelona.
Whatever the reason might be for him to play in PSG, the good thing was that he made himself a big name and was able to join a bigger team which he’s a man they depend on and hope that he will help them win a lot of trophies. Even in his new club, he was severally criticized and said to not be performing well and also called all sort of names. Many said he may pick up by next season but as we can see it, he was able to pick up form from this season and he’s now as important as any other player in the team that they need in any game they’re playing. I just felt he never adopted early into the team but when he did now, his performance is now paving ways for him and receiving all the praises he most deserved.