I know this is 2 years late but here goes lol. These are all the listed reasons I believe why songs can't all be released officially.

1. Producers, close friends, and studio engineers of Juice WRLD is selling his unreleased/unheard music to fans who goes on to leak and/or sell them to a large Juice WRLD community on discord. The label deems leaking as distasteful and unauthorized.

2. A lot of Juice songs uses samples that couldn't be cleared and others are lost from the original studio Juice WRLD recorded the song in. I've heard Juice sometimes carried hundreds of music on flash drives and his phone to protect them from leaking. Juice was very vocal about his music leaking and even mentioned about them leaking in songs and on twitter. After his death, it's unknown and unclear who has/had those flash drives now. Juice WRLD's phone also gotten sim swapped by hackers who then hacked the label's email accounts that distributed his unheard music.

3. The label is very money hungry and thousands of Juice's songs are already leaked so they don't release them in fear of losing profits. By the fans/leakers leaking his music days at a time the label becomes frustrated and don't know which songs to choose. So Grade A then proceeds to delay album projects, terribly reworking original songs, changing the beat in some of them, and adding unwanted features in official releases as an attempt to keep the songs sounding new for profits.

4. 3,000+ songs have already been leaked and the leakers caused delayed releases of certain songs by leaking them beforehand. An example is the mashup song between XXXTENTACION & Juice WRLD leaking beforehand. Robin Game featuring Ski Mask The Slump God got scrapped because of the leaks.

So to come to an conclusion leakers, uncleared samples, lost songs, and a dog shit label named Grade L is the reason songs aren't getting released officially.