The generation of the Dispersion sought to wage war against God and to replace Him. Why, then, was the punishment of the generation of the Dispersion less severe than the punishment of the generation of the flood, which was totally destroyed?

No survivors remained of the generation of the flood [other than Noah and his family], while survivors remained of the generation of the Dispersion although their sin was more severe. Because the generation of the flood was steeped in robbery, no survivors remained of them; but with regard to the generation of the Dispersion, because they loved each other, survivors remained of them. (Bereshit Rabba 38)