That's because most of them lack forsight, focussed as they are on their own power and little else. Not only are they narrow thinkers, but find their own failure inconceivable. If they were to consider that possibility, they'd probably think it an acceptable trade off for weakening a rival's access to information. We see them doing things that are detrimental to the war effort and the empire time and time again.
You still haven't convinced me how exactly would dissolution of Imperial Intelligence benefit them in any way. Both in short and long term they lose a great deal of personal power and influence. Are you implying they are self-destructive or even mentally challenged?