The same reason there are not constant assassination attempts in general: it’s outside the Overton Window of acceptable actions. One of the many benefits of civilization is that we’ve all agreed not to kill each other, even when it seems strategically beneficial in the short-term, because that’s what’s necessary to create the world we’d like to live in long-term. Defection against this norm is harshly punished to maintain the norm.
The same reason there are not constant assassination attempts in general: it’s outside the Overton Window of acceptable actions. One of the many benefits of civilization is that we’ve all agreed not to kill each other, even when it seems strategically beneficial in the short-term, because that’s what’s necessary to create the world we’d like to live in long-term. Defection against this norm is harshly punished to maintain the norm.