I think its because anger and frustration comes from a deeper place than more positive feelings. I know that sounds funny, but even love seems to come from just below the surface - you tingle and think of that person often, and yes, you do feel it powerfully, but rage and anger comes from deep within, strong, powerful, destructive even. Love and peace doesn't cause your entire body to go into fight mode where every muscle is poised to do something, now.
As any as any creative person is concerned, and this helps your audience remember you, is to have something of a point of focus, a hook even, to use an overwrought term. You have to find something important you, and then, much like with anger, tear it apart, disassemble it, by yourself, though, then, reassemble it in a new, clever, and thought provoking way -surprise people, give them something they've never seen, much like rage, for few people have seen the worst of that, and then, much like all the great writers, surprise them - explode their boring lives, give them something to think about, talk about.
Just saying... :)