Here's why:

* Major Mountain Ranges: The Rocky Mountains and Appalachian Mountains are the two most prominent mountain ranges in North America. They are indeed oriented roughly east to west, with the Rockies stretching from Canada to New Mexico and the Appalachians running from Alabama to Newfoundland.

* Other Landforms: However, North America has diverse landforms with different orientations:

* The Great Plains: Extend from the Rockies eastward, so technically north-south.

* The Canadian Shield: A vast, ancient, rocky plateau that covers much of Canada, with an irregular shape that doesn't neatly fit the east-west pattern.

* Coastal Ranges: Along the Pacific Coast, there are a series of mountain ranges that run more north-south.

* Mississippi River: This major river flows from north to south, creating the Mississippi River Valley.

Conclusion: While many major landforms in North America have a prominent east-west orientation, there are also significant landforms with different orientations.

It's important to remember that the Earth's surface is complex and varied, and simple generalizations like this can oversimplify the reality.