Because in Ligue 1, there is no team as strong as PSG. even without star players with names as big as Messi or Mbappe, they still dominate Ligue 1. if there is a team that threatens, it must be Marseille and Monaco, but with current points difference PSG does not need to worry too much. They just need to be very serious about the Champions League. They have enough difficulty there, facing strong teams that surprised them. They still have the potential to qualify, but hopefully, they can advance to the next round.
I think even the club management is no longer motivated to win Ligue 1 because they are almost certain to get it every season. It even seems like winning Ligue 1 is no longer an achievement that Luis Enrique as the head coach should be proud of. I mean the club management certainly wants to see PSG able to get a good performance in the UCL. Last season they managed to get through to the semifinals and I think that was a very good achievement for PSG. Unfortunately this season with the new UCL format they are in 25th place in the standings. With 3 matches left their only chance is to try to qualify for the playoffs.