My guess is Harden (or at least his people) has been trying to manipulate Philly to give him a max deal for a while now.
That's what all that nonsense throughout the season was that there was a strong possibility he would sign with Houston. It was really just to put pressure on Philly. Because guess what, it's free agent time now, and Houston apparently has no desire to pay Harden.
So Harden, going the scorched earth strategy and demands a trade, because nobody really has cap room to sign him. Now he's trying to find some other contender to move onto.
I think if Philly was going to pay him, he'd be more than happy to stay though.