The world at the time of Babel was not much different from the world at the time of the flood and God had every reason to drown this entire civilization with the exception of whatever few were true to him, but he didn’t do that. God promised that He would not destroy sinners in that fashion again, and that this was to be an age of grace and forbearance, so He dispersed them instead of destroying them. He scatters them over the whole earth and changes their language.