I don't blame the players or coach, I blame the league they're playing at. There's no competition in their league like there's no match you can look at and compare them to other top games in other leagues. In the premier league, there are multiple game you'll consider top games and this kind of games help clubs prepare for other top clubs from other league when they encounter them in competition like the champions league.
This top matches can also be found in other league like in la Liga, we have matches between Real Madrid vs Barcelona and Atletico, Premier league has Manchester City vs Liverpool, Chelsea etc, Bayern Munich has Dortmund to prepare them against top clubs from other league but what does PSG has, nobody. They can easily beat any team in their league with ease and this weaken their fighting spirit when they meet bigger teams and this is evident as they keep getting knockout.
But wait, PSG is not a team that is impossible to lose even though it has a number of expensive players in its squad. Last season PSG only managed to win 26 matches, 4 of which drew and 8 lost. This made them fail to win the 2020-2021 season title.
For this season PSG have also experienced 3 defeats and 5 draws in 28 matches. They are favorites in Ligue 1 every season which may be different from other leagues. But they are not a strong team in Europe where their failure is proof that they do not have good competition. There are only 2 candidates from Ligue 1 who qualify for the Champions League each season, and 1 other team has a chance of qualifying for the Champions League through the qualification pathway.