There is one major thread of thought that goes through and ties together the existentialists. They would not agree with the label but never the less it applies to all. Kierkegaard,  Husserl, Heidegger, Japers, Sartre,... That thread is the ultimate, absolute  importance of  "ME".  And to claim that this thought did not get accepted throughout the entire West is simply to be blind to the facts. Responsibility towards others, especially family is simply not even a thought that might occur to anyone. "It is all about me". It does not matter what religion anyone is. That is just the window dressing on what really matters to people; the ultimate, absolute "ME.

You might see this in all of them, but it becomes particularly clear in Heidegger-''Being'' instead of God. Responsibility is only to :"My Being" :i,e., to be authentic to  ME.