Feels like having great players doesn't guarantee you any success, also not everyone season is like the next. Real Madrid knows how to play in this tournament, even in the years they are not amazing, they still managed win and they will keep being that good because they bring in the younger players at the bench to grow up with older ones getting the title, so they put that UCL title winner mindset into the younger generation, and when older generation retires, the younger ones already have a few cups with them.
So all in all, I think we should consider that PSG İs missing that winning culture, the stress they have when they are at knockout stages of UCL is showing and they always miss shots that they would normally score.
Only happening for PSG because several teams support great players success winning Champion League such as Manchester City won its las two season ago.
I think PSG need improving not only their performance but also winning mentality when playing in Champion League, this season had not bad achievement after success qualifying until semifinal round but unbelievable defeated by Dortmund back to back on away and home matches.
For domestic league, have been easily keep dominance every season for PSG but have to make difference with their performance when playing in Champion League. PSG the only one team spent much money and sign many star players but never winning Champion League trophy yet until right now.