Why did nelson a Rockefeller have Diego rivera's fresco man at the crossroads looking with hope and high vision to a new and better future destroyed?

Because it included an image of Lenin and a Soviet Russian Mayday parade. At the time, it was seen as very anti-capitalistic Propaganda.

Rivera however, recreated the mural in Mexico City with some changes: it also included Trotsky, Marx and Engels and in a serious take that display, he also included John T. Rockefeller (Nelson Rockefeller's father) drinking with a woman with a dish of syphilis bacteria on top of them.