I don't what to speculate but it should be around the money I guess. Maybe he was promised to have a good money this season. But the owner turn his back on Harden.
Words are very powerful, and they should be honored. If James Harden is promised good money without conditions, then he is due for that. However, sometimes these businessmen are very clever; they tend to use their power to influence a player's decision but ultimately may not stand by their words. Nowadays, the system has already changed, as players can make demands. In the case of James Harden, being a superstar, I'm pretty sure he knows what he's doing. He understands that he won't lose his job, even if the 76ers decide to trade him, which they have refused to do until now.
NBA = business. That's what these businessmen see the league right now. On the other hand, there are these players who are acting like they're the boss of their own team, and demands a trade if they wanted to, or speak if they wanted to.
With regards to Harden, I guess the Sixers don't want to trade him anymore, or at least at the start of the season depending on how he will act at the start of the season until the mid-season. Harden already said that he will not play with the Sixers, and the team don't want to believe in him since he's on his last contract already. If Harden will not play, there's a high chance that his value will go down, and other teams will give him lower contract. I know that Harden is a superstar, but he's a player with lots of drama on his back, and his demand isn't as high as that of Durant, or even Irving or whatever superstar it is.
If there's any team that will be interested in him, it would be teams that's desperate of winning a title that what they only needs is a Point Guard who can run the team. Teams like the Lakers, and the Clippers are the 2 teams that I think he will be fit in, but between the 2, I would pick the Lakers. I mean AD, Lebron, and Harden with the same team is just a good team. The Lakers don't have a PG right now since they've traded Schroeder already. I guess if the Sixers will trade him mid-season, I just hope that he will go to the Lakers.