Because if you keep them in the dark they don’t know what you’ve got. you can use what they don’t know or are afraid of what you may have... both of which can be used to leverage and manipulate people into turning on each other. Perhaps even turning or releasing state’s evidence providing locations, dates, times into narratives more accurately and basically destroying the traitors because they don’t know either what you know or dont.
But they just KNOW you may have something that could do them in.
Fear and pride: The two gifts that just keep on giving!!
From a Tom Clancy novel:
"You know what they just did? They dropped a torpedo to spook us into moving. They know we can't afford to ignore a torpedo."