Sartre’s early work is brisk and authentic. In it, he advocates existentialism, this being the doctrine that one must choose one’s values for oneself—which, though seemingly nihilistic, is actually an anti-nihilistic way of dealing with circumstances in which values are not readily available and must therefore be forged.
During this phase, Sartre produced The Transcendence of the Ego, Being and Nothingness, and The Imagination, along with other, similarly focused and coherent works.
Then what happened is—he sold out.
He sold out to the bogus 1960’s pseudo-counterculture (i.e. the establishment posing as anti-establishment), which involved him embracing Marxism—the essence of which is that one’s identity is not of one’s own choosing but is bequeathed to one by one’s social class, ethnicity, gender, and the like.
So Sartre had a problem.
He had to reconcile his first message (‘you are what you make of yourself’) with the Marxist message (‘you are not what you make of yourself’)—which he couldn’t do, obviously, since it cannot be done.
But he wouldn’t admit this to himself, since his icon-status was predicated on his continuing to toe the ‘counterculture’, junk-culture ‘Marxist’ line.
So the books he ‘wrote’ were really books that he was simply trying to write—but couldn’t, since there was no longer a coherent angle there for him. And they consequently just went on and on and on—and said nothing while doing so.
‘Critique of Dialectical Reasoning’ is one of the most dismal failures of intellectual history, almost on a par with Edmund’s Husserl’s ‘work.’
Long story short: Sartre sold out. And when people sell out, they die inside, and their work is a pale imitation of what it once was. There is no way to split that difference—but that doesn’t stop people from trying.