Something always troubled me about Mike Hayden but I could never put my finger on what it was... that is until a couple of days ago:
Putting the serious hat on for a second, the two Directorates have had good cause to remain separate. For starters, there's the question of OPSEC- DI analysts typically are not privy to the precise sources and methods used unless it is absolutely necessary. Secondly there's the concern that an analyst's judgement can be clouded if they have an attachment to a particular aspect of an operation.
For example, the DI at CIA was screaming from the rooftops (quite correctly) that Ahmed Chalabi was a big-timing cnut and the int they got from his peeps at the INC was dodgier than a 3 week old curry (not their exact words, but you get the general idea). Would they have made the same assessment if they had a hand in running them?