Isolated in their ivory towers, the academics pass their lives writing obscure theses which are read, and sometimes answered, by other academics. Few people understand what they write. Let us take Existentialism. Existentialism has its roots in the irrationalist trend of 19th century philosophy, typified by Nietzsche and Kierkegaard. It has assumed the most varied forms and political colouring.
Existentialism centres everything on the moment.
All that you can achieve is in the moment in which you are living and anything before or after becomes irrelevant. It is an individualistic and extremely pessimistic view of the world, entirely at one with the psychology of the petty bourgeois intellectual. This is the very opposite of Marxism and inevitably leads you away from a class understanding. Thus it becomes irrelevant to study the past, to study overall processes. You must live for the moment and for yourself.