If he stays at PSG, it means Qatar has something great planned for PSG for their World Cup year, it's not about money, Mbappe will be extremely rich whatever happens, he doesn't care about that.
It would probably mean PSG is about to recruit great players, that's what Mbappe cares about. Outside of Verratti their midfield has always been very average. As an "ally" of UEFA during the SuperLeague failed revolt, they'll have more headway on the transfer and spending front.
Mbappe probably really wants to leave his birth place (he was born in Bondy, close to Paris) AFTER making them win the UCL, or at least try a last time with better players.
It would have the added bonus of allowing PSG to get some money back when he leaves for RM, which would probably be next year. That's something that probably matters for him too.
Still, in my opinion, for his career, he should leave now. It's ridiculous watching him play in Ligue 1 right now, like a world beater playing with kids. He's wasting part of his huge potential. His place is in Liga or PL...