WW2: Heidegger is the premier, German philosopher. And he's a Nazi. So the question is: what does it mean for the projector of philosophy that the leading light is also a fascist? Enter Satre who "rejects" Heigger but "keeps" with Hegel.

Being and Nothingness, as far as I understand, was a response in part to Heidegger's Being and Time.

My philosophy may be rusty, but to answer the question you asked, I think history is the reason why others held him in regard.