What made people move West to make money in the US?

One, it became too crowded in the East, from east of the Appalachian Mountains and associated chains that pass through the New England States, through Middle Atlantic States, and through Southern areas to Georgia.
Two, the government offered free or low cost lands to settlers moving West.

Three, Manifest Destiny was the idea that people owned from "sea to sea" (ocean to ocean) and they were meant to spread out and take control / take over.