While there has been no official confirmation that was the reason, it seems that Vinicius Junior finished second in the ballon d'Or poll to Rodri Hernandez was behind the non-assistance of Real Madrid. Vinicius posted after the winner was announced that he was going “10x over” afterwards, and generally seemed upset by the verdict.
He ensured after the Best award, which he won, that he was now the best player in the world. While the Ballon d'Or might have damaged his ego, there are a million other reasons Vinicius could be frustrated by the verdict.
AS Diary details that Vinicius will go from earning 15 million euros per year to 20 million euros per year in the last two years of his contract (which runs until 2027), a significant bump of 33% and a difference of 10 million of euros in total. The Best award activated bonuses in his contract, and it is assumed that the Ballon d'Or award would have activated the same, or perhaps even meant more bonuses.
Clearly, this is all related to your earnings, but most would be disappointed at the prospect of losing 10 million euros, beyond the general hope that he had to win the prize. Los Blancos are set to offer a new deal next summer, amid interest from Saudi Arabia, as he moves into the final stages of his contract. It's worth noting that some outlets dispute Vinicius' current base salary, saying it's closer to 10 million euros a year.