Why are the US states on the east coast smaller than the ones on the west coast?

When the U.S. first expanded beyond the first colonies, many of those states automatically claimed the land that was west of them as theirs. Imagine a Virginia that reached the Mississippi, or a Detroit, New York.

In the early years of a country it already had other parts of states become new ones like Vermont from New York, and Maine from Massachusetts. So when the new lands were gained from the French. Many of the land was already in use. Places along the Mississippi river were already bustling towns. The mountainous borders of Appalachians had already become hinge to many Scott-Irish. It's why many of the second rush of states are not much larger than the east coast ones.

The states beyond the Mississippi are large for a few reasons. The first is due to their relatively low populations. Becoming a state requires a minimum amount. The second reason was because of the pending civil war. New States could help either side. The third reason was to break up Texas, which used to be much larger. Stars like California were created so large with the goal to make smaller states later on, northern California was supposed to become the state of Jefferson, but WW2 broke out and it just never happened.