See this aerial view from google maps. Massanutten is in the foreground, as straight as an arrow. The Appalachians are on either side, looking like more typical mountains, zig-zagging with outcroppings in every direction. I was lucky enough to find this video on exactly this topic, but I have zero geology knowledge, so it went completely over my head. Can anyone explain it in very simple terms?
If you look a wider view from above and a bit to the west, you will notice Massanutten is not that straight nor is it unique most of the surrounding mountains are the same, especially to west. Basically you camera is pointed in exactly the wrong direction to see the other mountains.
You can picture the appalachians as a flat section of rock that has been compressed like an accordion east to west, that's why they are more or less parallel, but not perfectly parallel becasue the rock is not completely uniform in strength or hardness. Plus the compression has a bit of a curve to it making it even less uniform.