District Court Divisions

Here's a curiosity. Taking a look at a map of the federal circuits, it seems like there are some pretty strange disparities in the number of districts into which states are divided. I don't know if it is a matter of population shifts outpacing boundary drawing, differences in how the population is spread throughout each state, or some crop circle-like alien disturbance.

But there is something unusual about states like Colorado (4.6m pop.), Minnesota (5.1m), Arizona (5.7m), and Massachusetts (6.1m) having only one statewide district, while Oklahoma (3.5m), Alabama (4.5m) and Tennessee (5.9m) each have three. Even West Virginia (1.8m), Arkansas (2.7m), and Iowa (2.9m) have two districts. What the heck is going on?

UPDATE: Will Baude emailed to let me know he recently pondered the same question and got some interesting responses.