I believe Mbappe will have put into consideration so many things before he still want to remain in PSG. The pay is fat and he is still the most expensive player in the world. He believes that he still owes PSG and needs to complete his contract with them. He is a superstar that has a good potential and I know that PSG wouldn't let him go easily.
Mbappe should start thinking on how to win UCL and also win other trophies so that he will have the dreams of playing in Real Madrid after the end of his contract with PSG. Other clubs needs his skill and contributions to the team work and he shouldn't just be static in his football career.
Apart from a superstar that has a good potential, he is also one of the players who is skill at create controversy
For example, before signing a contract extension with Paris Saint Germain in the 2021-22 season, he had also express something similar regarding his desire to play for Real Madrid and feel the warmth of the UCL trophy. It was conclude as a signal because at that time Real Madrid had also open negotiations with him, but everyone know that the opposite had happen.