Somebody is actually looking for logic in air fare pricing?

It's based on all the above factors, plus more - such as:

- the degree to which flights tend to be a matter of choice. Florida is often cheap because vacationers who go there could go somewhere else instead. Flights that draw mostly business travelers tend to cost more per mile.

- overall demand on the route, which can allow airlines to use larger aircraft - reducing cost per mile, if they can fill them, in turn reinforcing lower pricing to attract passengers.

(As an example of the Florida effect, I recently flew BOS-SEA with no Saturday night stay. Connecting through Chicago westbound, AA's fare was $400 less via Orlando than with a BOS-ORD nonstop, with the same flight ORD-SEA. Go figure. (As a loyal FT'er, I took the savings and the miles.)