We are not sure yet, maybe Mbappe is just doing that to make his team spend more for him and increase his salary. Right now are see much news about PSG wanting to increase the salary of Mbappe and keep him in the team for the next season. That's why they did it the last time and it's not surprising to see the same story.
Even before the end of the last season, PSG did not give Mbappe as much importance as before the start of the new season. PSG has already agreed to the offer made to PSG and PSG wants to sell this high priced Mbappe to the Saudi League but so far there is no such news from Mbappe. PSG believe that Mbappe has secretly completed a deal with Real Madrid, which is why Mbappe is not so important at the moment. PSG is treating Mbappe the same way PSG treated Messi a few days ago. Where Mbappe was planned to form a new team at the end of last season, PSG toured Japan without Mbappe, so it means that PSG is no longer planning on Mbappe.