How and why did they “leave off to build the city” (Gen 11:8) of Babylon?

Indeed, since the city was Babylon, was the city construction temporarily halted, only to begin again later, or what? Probably what is meant is that the “city” then being planned, because it would include all people then alive, was going to be far greater and more splendid than the one that emerged, which included (perhaps) only Nimrod and his followers.