Minnesota being different from surrounding states is likely from Walmart/Sam's not wanting to encroach on Target as much (relative to Costco competing there), with Target's HQ being in Minneapolis. To another poster's point, BJ's has a strong presence in mid-Atlantic and Northeast.

I wonder how much of the differences in profitability, sales per retail location (or sales per square foot), average employee pay, retail prices, etc. between Costco and Sam's are attributable to geographic footprint and how much from actual operations or strategic decisions (likely a strong mix of both). In some ways Sam's is kneecapping itself also by frequently sharing parking lots with Walmarts.

BTW the Sam's Club blue/green logo used in the graphic is outdated, not their current design. (That said the old one depicted is more recognizable.)