https://www.gamespot.com/articles/e3-2018-death-note-characters-arent-playable-in-ju/1100-6459838/

Jump Force was revealed during Microsoft's E3 press conference and got many fans of the respective manga/anime hyped up for this arena brawler. Naruto, Dragon Ball, One Piece, and Death Note somehow come together in a three-on-three tag action fighting game, but it was confirmed during an interview with game producer Koji Nakajima that Death characters are there to setup the story, but not fight.

Nakajima said (through translation) stated, "This game is going to feature a story around this unique situation, and that's where Death Note comes into play. To kind of weave the story together. So, Death Note is not [going to have] a fighting game character." Unfortunately, Nakajima wasn't able to talk more about the story during the interview.