Systems of Oppression

Our discussion on animal rights reminds me that all systems of oppression are connected. You cannot separate racism, sexism, classism, speciesism, or any other form of oppression. Bell hooks, a writer who focuses on the intersection of race, class, and sex, calls this ultimate system of oppression the "imperialist white-supremacist capitalist patriarchy". These different forms of oppression are not mutually exclusive. So, to stick up for one oppressed group, you must stick up for all of them. The ultimate enemy will always be the same thing. The human domination of other species is directly related to male domination, racial domination, class domination, etc.

Question: Why do so many people only care about the issues of one oppressed group, instead of all of them?