While I don't agree with most of their reasoning, I do understand some of it.
If a large male has x miles of territory that he defends then the younger cats need to find new territory. If the large tom is removed then two, maybe more, younger cats can use that same amount of space.
Just like coyotes. If you have a pack that controls a large piece of land and kill the alpha male or pair then often you will end up with two packs sharing the same piece of land.