Funny how Brazilian players are the extreme opposite.
By the way. I've hears Mbappe still have crazy amount of goals yearly. So I really doubt if he is the problem or if coaches don't know how to use him properly.
I think with national team patriotic fervor takes over. Whole Nation has hope and wishes for you. As WC happens once in 4 years and is much more prestigious than any other trophy, I guess most players simply put everything aside - rivalry, tensions, ego for the sake of the team and work as a unit.
With WC it's not about the money or ego for such people but Nation's glory and cement one's legacy.
With Clubs it becomes more personal - more ego and pride driven. More big names a team has, more difficult it becomes for coach to make a strategy.