After joining PSC, Lionel Messi did not get the same support as the rest of the players supported him when he was in the Barcelona team. As a result, Lionel Messi is failing to give PSG something extraordinary. But I will blame the coach of the team for the bad condition of the team.
Or maybe it is about the fact that Messi is getting older as well. I am not really considering Messi to be someone that plays badly, but that doesn't mean that he is not playing as amazing as he used to. He is still playing very well, and he is still playing better than most players in the world. However, going from "greatest football player of all time" down to "he is at least as good as Kevin De Bruyne" type of level, is looking like a drop anyway.
Yes, it is a drop but would you not want him on your team? Any team in the world would want him still, dude is a beast, he is not GOAT level anymore but still better than any player in any team and that's why I think it may not be the reason why they haven't done well.