If they wanted to run projects like PSg in the premier league they had to spend much more money because in the premier league, there are many ort rich teams and there is a closer race between other teams while in the French League, they could have easier days, if they were spending this money in premier they could even lose the top of the table easily.
That is exactly the point and that is why I am not a big fan of picking a league that is inferior and then invest a billion and celebrate the team for winning the title on a yearly basis. Not a lot of people are truly excited when they can watch Neymar, Messi and Mbappe play against Troyes. But what if they hypothetically be playing for Newcastle instead and people get to see them to play against Manchester United / City, Liverpool, Tottenham, Chelsea etc. Having those three guys play for the Ligue 1 title in the same team became very boring over time. Everyone was waiting for half a year to pass until the knockout games in the Champions League finally began and if PSG got eliminated early, then the season was essentially over.