I think Dio is fighting some inner demons (instead of the ones in his songs)...
He's lost his edge or something.
Tenacious D said it best:

"Dio has rocked for a long, long time,
Now it's time for him to pass the torch.
He has songs of wildebeests and angels,
He has soared on the wings of a demon.

It's time to pass the torch,
You're too old to rock, no more rockin' for you.
We're takin' you to a home,
But we will sing a song about you."