There are some misconceptions here.

Most rental locations are corporate-operated, using a pooled fleet that randomly circulates the country. So that car in MCO with GA plates might have started out in Atlanta, but came to FL from TN, for instance.

Cars are usually not "sent back" after a one-way, unless an independent licensee is involved. That's why you see so many out of state plates at rental lots in large cities, where a lot of people visit, move to, etc.

Rates are based on supply, demand, and minimum estimated mileage. Ex, It's usually cheaper to rent one-way from a small market to a larger one than vice versa. What matters is flow. Seasonal demand shifts are another part of that.