What existentialism was lacking is treatment of its ideas into an expansive and systematic work that academics could recognize.
Of all the existentialists it was Heidegger (1889-1976) who was purely and academic.
Although many of the ideas within his philosophy are radical even revolutionary.
He had focused his ideas on such existentialist themes such as:
The importance of interpretation,
Living authentically and the significance of death in defining human existence.
It was Heidegger who put the exist into existentialism.
Heidegger was not only concerned with living but also with what it means to be (as opposed to not be).
In one sense he made existentialism into a science of being.
Yet starting as it does for the subjective point of view, it’s a science that never objectifies human beings.