Possible Explanation 3 — Nothing is wrong, they just don’t trust the process
Maybe everything is fine but like all of us, Brett Brown and Bryan Colangelo cannot bring themselves to risk a jinx by declaring him good to go. Sports are notoriously superstitious and these guys career success is so tied to a healthy Joel Embiid they are simply afraid to claim full health.
Just as we were all dead when it was reported that his Navicular bone had separated again and would require a second surgery, perhaps Brown and Colangelo would be so devastated that they simply cannot bring themselves to publicly give a thumbs up.
Possible Explanation 4 — Something is still wrong
This is depressing to even consider, but perhaps Joel is still experiencing minor swelling after workouts over multiple days. Six months after surgery, this would be disheartening because it essentially means that his knees will continue to be an issue and likely slow him down and/or shorten his career.
It would explain why the team wants to limit his workload and maximize the miles left in his body. It doesnt necessarily mean extended time missed, but it means he will likely continue to not play back to backs, and very likely play less than the 60 or so games I think he would need to play for the Philadelphia 76ers to reasonably compete for a playoff spot this season.