One for the price of two

Ok, I give notice this morning and then went looking for plane tickets home! Can anyone tell me how in the hell can a one-way plane ticket cost twice as much as a return ticket. That annoys me as much as a time limited return bus tickets. I mean you've paid for the return ticket so why should you not able to use it whenever you want! I can understand a specific time for long-haul plane tickets but buses?! Grrr. Chewbacca defence.