You crazy people!!! Trying to make sense out airline fares!! Pretty silly, eh?
The (he, he) fact is that one way fares are higher as they cost almost as much to ticket as round trips and yet they still have to book "that" seat back (or empty) and if booked, have to pay to administer that transaction too.
Also (again tongue in cheek) if you only book one way they do not know if you will stay over a Saturday night or not!!
Why, not even two people on the same plane, both traveling one way (the same way, too) will usually be paying different fares!!
Fares are only fair to the fare collector, and occasionally to the faree, if the price seems fair. Now is that a fair fare or unfair?