Why are there so few friendly matches between the club and the national team?

Because the national team competition (including the official friendly match on the national team competition day stipulated by FIFA) is graded, it is related to the ranking of the national team. The higher the ranking, sometimes it is related to drawing lots and grouping, so it generally does not compete with clubs without scores.

At the same time, there will be duplication between the national team and the club. Every member of the national team is made up of excellent members of the club. For example, when Barcelona and Spain play a friendly match, Barcelona's Spanish players Savi, Inesta, Fabregas, Puyol, Alba and Pique all have conflicts about who they play for.