Two years ago, Carl Jones was on a podcast where he explained why he left The Boondocks.
The show was originally supposed to end after season three, but Sony Pictures ordered 20 more episodes for a fourth season. Carl was working on Black Dynamite at the time and Aaron didn't like it. Carl was never going to leave The Boondocks and was just working on Black Dynamite on the side, but Aaron told him that he had to pick one or the other and he chose Black Dynamite.
This ended up being a problem because Carl was responsible for certain aspects of the production of The Boondocks, and since he left, Aaron had to take over those responsibilities along with the work he already did. Season four ended up being way behind schedule because of how long it was taking to get everything done, and Carl wanted to come back to the show to help out but Aaron wouldn't let him. This is why only ten episodes were made instead of twenty, and Aaron ended up deciding to remove his name from the fourth season entirely. He actually did work on some of the episodes that came out, he just didn't take credit for anything. And we'll never know how much work he did or what episodes he wrote specifically.
There's a chance that Carl will be interested in working on the Boondocks reboot, but right now, he's working on the show Sugar and Toys. And even if he ends up being free, I feel like Aaron is the kind of person to hold grudges, so he might not want Carl's help at all and we could have another bad situation on our hands.