I think it was more so the Clippers not wanting to do the deal and give up what assets they do have left than Philly because of the uncertainty around the future of PG and Kawhi.
Its four things:
1. We resigned Westbrook
2. Harden or no Harden, a deep playoff run still relies on PG & Kawhi being healthy in the post season.
3. Mann needs more minutes and its time to see if Bones and Brandon Boston can add anything to the team. Plus they're on super cheap deals
4. Since Harden prefers the Clipps only, we can't bid against ourselves. And this is more about Harden wanting the Clipps as opposed to the Clipps wanting Harden.
-But in all fairness, if this was prime "Houston Harden" or if he was simply known to beast in the post season this deal would've been done a long time ago.