Apparently you did not follow this story well, since in the end the transition did not take place only because of De Jong's decision to stay in Barcelona. Barcelona would have been happy to sell him (and be free of a huge salary obligation) and United to buy him, but De Jong himself didn't want to go to a club that didn't play in the Champions League plus his girlfriend was against leaving Barcelona for England.
The speculation that occurred on De Jong transfers was full of controversy and also took a lot of time, Barcelona had actually agreed on De Jong move to Manchester United but reportedly De Jong actually rejected the move for unknown reasons, but Barcelona reportedly has a debt to De Jong made it possible for De Jong to intervene in Barcelona decision so that the agreement with Manchester united was canceled at this time, reportedly also De Jong did not want a move and also did not want to cut his salary so this caused confusion for Barcelona.
How can one speak of "unknown reasons" when on the surface there are several reasons why this transition was unprofitable for De Jong? Debts that Barcelona owe him + demotion in class (I'm a United fan, but now moving from Barcelona to United that doesn't even play in the Champions League is a demotion in class) + his girlfriend who prefers Spain.