Cable wasnt targeted by the Death Commandos in End of Greys bc he wasnt at the family reunion PERIOD. It was an attack that happened over the course of a few minutes and he wasnt present. The Shi'ar did not go dn target any individual Grey; they all just conveniently happened to be in the same place at the same time. Cable was a 50 something year old man and he doesnt yearn for a family and sense of acceptance the way a young college aged Rachel did which is why he likely wasnt there. There wasnt any big conspiracy. That just wasnt his thing. I dont ever recall him ever even meeting or interacting with the Greys and really had no reason to with Jean dead at the time. It makes more sense that he would be detached and find going to a family reunion for people he doesnt know to be meaningless and a waste of his time