English settlers arrived in the east. So wherever they were when they named an area, that was the original, and as they spread west, north or south, they had to add those directions to keep them distinct.

Serious answer: we started at the eastern seaboard and expanded west. "East Statename" implies eastern expansion.

That's because the expansion of the US across the continent was westward.

Are there any 'West _____' states? I know there are north and south