You're asking why I, the Overlord of Eravate, would want as many people as possible to know about my reign of terror? Because my power derives from others fearing me; the more people that fear me, the more my power grows.
Why do politicians campaign and advertise themselves? Couldn't they humbley stay at home, and not mention their aspirations of power to anyone, in order to avoid "blowing their own horn"? They could do that. And they would never acquire any power if they did.
I'm just entertained that you took the time out of your day to brag about the fact that you would never "blow your own horn"...except that you did in that very sentence, brag about your humility.