That's always been my theory. The guy was a notorious workaholic, especially after he moved to L.A. and started getting TV assignments.
There's plenty other things he did where it was obvious that he was turning in competent but not really inspiring work in return for a competent but inspiring-enough paycheck. But hey, such is life, no?
And when he was inspired, whoa.
Sadly (really, really beyond sadly) he took the "whatever" route with the Monk album. I have trouble forgetting that.