Why buying a 2 way ticketscan sometimes be cheaper than a single way ticket?

Maybe more info would help get some more responses. What is a ticketscan? do you have an example of a 2-way being cheaper than a single?

I’d say it’s like nearly everything else: if you buy more, you get a greater discount.

Economies of scale play a major role. Buying more of anything means that they are guaranteed more money, so they don’t feel that they would have to charge as much.

The airline, knowing you are going one way, would rather give you a discount for a round trip because they no longer have to worry about filling that seat on the return trip.

If they didn’t sell you the roundtrip, they may or may not find a buyer for the return seat.
Sort of a bird in hand point of view.

I still don’t get it. Its like getting a free return ticket by buying a single journey ticket. Why would they want to fill up the return flight space even though they are not earning? Moreover, it only drains more fuel with additional passenger and luggage.

@Suanne You will sometimes get this sort of offer from airlines, rail and bus services.

Are you saying that you are getting a round trip for the cost of a one way trip?
If so, that’s also easy to explain. Airlines have pretty good data to estimate trip loads. In your case, they may have data that suggests your seat is likely to be empty. By offering you a return free, they have bought some good will from you and denied profit (you) from competitors. Since the only unpaid weight on an airline is humans, your additional weight isn’t going to affect the fuel cost too much (and their fuel surchages may be based on higher fuel prices than exist now).

Usually the return trip isn’t free.