I personally don't think its any one thing, but a combination of circumstances and not necessarily the same combination for each of the efforts you're speaking too.

He's had a ton of uneven albums released, while leaving some quality material on the cutting room floor in the process. I don't think he never quite met his A&R muse and frnakly for all his lyrical talent purhaps he's simply been trying to go to far to fast for his core audience.