It is a pity that Frenkie de Jong ultimately stayed at Barcelona. He also seems to be a kind of 2nd choice there and will often start on the couch. At Chelsea or United, he would certainly have become a base player.
Although he is the second choice in Barcelona squad, he can play with quality players. He also seems suitable with Xavi tactics, so he feels comfortable staying in Barcelona. While if he moves to Man United or Chelsea, he will be the main player but may not be suitable with the tactics of the coach on these clubs. He also may feel uncomfortable with a bad situation the new clubs, especially Man United or Chelsea. These clubs are in a very bad situation this season.