Could be any number of reasons. He's an ex navy seal, and an admiral. He has value. Being out in public makes him a target. I've always thought the guy who portrayed Chris Kyle publicly wasn't actually Chris Kyle. I think the real Chris Kyle "died" so that he could retire without having to walk around with a target on his head. Or he was killed because he knew too much.
With high security clearance people you really don't know what the motivations behind their actions are. Why did Chris Kyle lie about Jessie Ventura in his book? What was the motivation? Political takedown? Personal vendetta? Chris being drunk at the time and having a fuzzy memory? Nothing seemingly makes sense in a lot of these cases.
