The Shifting Geographical Center of US Population

Maybe this is the kind of factoid that is only of interest to me, but the US Bureau of the Census calculates the "mean center of population for the United States"--that is, if you average the locations where everyone lives in the US, what's the average location?

Back in 1790, the average location of the population was near Washington, DC. Unsurprisingly, over time the center of the population moved west, as additional western states were added.

I found myself mildly surprised by three factors about the movement of the average location of an American in the last couple of centuries.

1) I'm surprised that the center of the US population was already in Maryland in 1790. I would have thought that with a substantial share of the population in Philadelphia and New York, as well as Boston and New England, that the central location in 1790would have been further north.
2) I'm surprised that the movement has continued at such a steady pace in recent decades.
3) I'm surprised that the average location of the population has reached the middle of Missouri, apparently headed for Oklahoma in another couple of decades.