They essentially explain their issue with Okafor, right here:
Philly has been outscored by a staggering 19.2 points per 100 possessions with Okafor on the court. If any team played an entire season that poorly, it would shatter the all-time record for futility.
Okafor has little talent around him. The talent he does have, he makes even worse with his horrific defense and black-hole mentality. The problem isn't that he hasn't elevated the Sixers, the problem is that he's made them worse at times.
My problem with this is holding a rookie to that standard where you expect them to make their team better regardless of the talent around them, or the composition of that talent.
Ever think that the reason the Sixers are so much better without Okafor on the floor might have something to do with just how terribly they are built to play a halfcourt game with Okafor posting up on one end and functioning as the last line of defense on the other?
You have to remember that, to the extent there are players with NBA level experience on that team, they've all come up in a system where they've been taught to just fly up and down the court, get into passing lanes, and constantly look to attack the basket. In so many ways, they are not set up to succeed in a slower half-court game (which is much harder for young players to learn).
Putting all of the causal emphasis on the individual player for how the team does while they are on the floor is asinine. This is a problem I have with plus-minus stats in general. There is a strong tendency to take them to mean far more than they do, or at least to disregard the variety of things that they could mean.
As for the "he's not a perennial All-Star like they thought," thing, well, if they thought that was a guarantee they're stupid.
The comps for Okafor all along have been guys like Big Al, Greg Monroe, Brook Lopez, and best case scenario Pau Gasol.
Back to the basket centers are going out of style in the NBA, but I have no doubt that teams can still have success with talented scorers at the 5 like I just mentioned. But it requires you to have a team that's properly built to function around a post scorer, and the skillset of players coming into the league is generally not skewed toward succeeding in that type of setup.
So you need to have a guy that's good enough to justify building your offense that way. I think Okafor absolutely can be. But expecting him to raise the play of the team around him when the team around him is pretty much tailor made to emphasize his weaknesses and fail to take advantage of his strengths ... the problem there is not Okafor, it's you.