Because if he really has the motivation for that, it is clear that he will easily move to Madrid, which is most likely very capable of paving the way for Mbappe to achieve all of that. On the other hand, PSG does have a bad relationship with Madrid regarding player transfer matters.
Until now, Madrid's focus has been on finding alternative CBs to provide backup for injured main players, especially in the back line. Moreover, next season Endrick will clearly join the senior team like Arda Guler did.
This drama got everyone sick of it a year ago, but it's still being talked about. Some say that Mbappe will definitely move to Real, that he has already all the verbal agreements and so on, and some do not believe in his transition because of the love of money. So I don't think money is a problem for Real Madrid, if they really want this player so much, according to rumours his salary will be 35 million a year, isn't that enough? It's even too much
When it comes to whether Real Madrid have the capacity to buy Kylian Mbappé right now, I think they do. If they truly want him to enhance their team with his pace, they will make it happen as soon as possible. On the other hand, if Mbappé is ready to join Real Madrid to boost his career and pursue more trophies and tougher games, he would gladly accept because they are promising.
I don't think it should be all about money. Another factor that Kylian Mbappé might consider is the opportunity he used to have in the PSG club to determine who features in the starting lineup for every match. The level of autonomy given to him in PSG may influence his decision to join Real Madrid. I don't think many clubs offer such opportunities and privileges, so maybe that could be another factor he is considering. But on the brighter side, if he is ready to work towards success and fame, joining Real Madrid could be a great move.