Of the "main" US highways (i.e. the one- and two-digit routes), the longest nine were all east-west routes (6, 20, 50, 30, 40, 60, 70, 80, 12). And if we take the longest 16 highways, only one of them is a north-south route (US 1, shown in red here):
That stands to reason, because the United States is roughly twice as wide from east to west as it is from north to south. So it makes sense that there would be more long east-west routes.