Airlines usually either don't allow the transferring of tickets to another person after they've been purchased, or they do it at an extremely inflated price. What is the reason for doing this?
One idea I came up with would be to allow authorities to do background checks, but one could buy a ticket at the airport shortly before the flight. Of course, it would be more expensive and there would be the risk of a fully booked plane, but it is not impossible.
Airlines have a pricing strategy known as "yield management" or "revenue management" - they charge less for some seats than others, and expect these seats to be bought a long time in advance. They know that only a certain percentage of their customers are able to buy seats well in advance, and that those customers wouldn't fly if they couldn't get inexpensive seats.
A speculator could buy a $100 ticket and then offer it on eBay close to the flight date for $200. If more than half the seats this speculator bought were sold this way, the speculator would be making money. But the airline, which wants to sell seats close to the flight date for $500, would not. In fact very quickly the speculator enjoying selling 75% of tickets for $200 would see it fall to 0% because of another speculator selling them for $150, and then later another for $110 and so on. This is just how reselling markets tend to work.
By insisting that a ticket is not a commodity to be bought, traded, resold, and passed around from hand to hand, the airline is able to keep its complicated pricing structure in place. Overall, this is a good thing, because those last-minute high-price tickets cover a LOT of the cost of the flight - their existence is what keeps the long-advance-notice tickets so cheap!
Another factor--sometimes life happens and you can't fly. In the old days you could simply sell your ticket to someone else, now you either have to eat a hefty change fee or lose it outright. That's money in their pockets that they didn't use to get.
Airlines aren't just in the business of selling "tickets" to seats. They are selling tickets to seats on different days. It's the "different days's" part that means that the same seat will sell for a lower price "in advance" and a higher price closer to the flight date.
If you could re-sell the ticket to a friend, you could (theoretically) get the advantage of the "different days." More to the point, speculators could do the same. The airline doesn't want to allow this opportunity.
The best solution is for the airline to refund your "cheap" ticket, so they can re-sell the same ticket at a higher price on a "different day" to another passenger. Many airlines will do this. Some will not, because they don't value customer service/relations enough.
This may result in an abuse situation. You can think that a non-registered travel group bought so many tickets with different names on a certain flight, then start selling the tickets but for larger price.
Unchangeable tickets will get rid of this situation and only registered travel companies can have legal deals with the airlines.
Another reason might be that airlines tend to overbook planes, if they can. They expect a certain percentage of passengers to cancel their flight and want to prevent empty seats. If everyone found a replacement, there would not be enough seats on the plane for everyone!
I realize there's already an accepted answer about "yield management" but, while their price discrimination strategy certainly exacerbates their rationale, I think that misses the point. I think the bigger reason is quite simply that they can get away with it. Let me expand on that. When most people book an airline ticket it's because they're planning to fly themselves so they discount the chances that they'd want to transfer the ticket to someone else. This means when most people book a flight they're completely willing to agree that the seat they're buying can only be used by them even though objectively that's an unreasonable condition of the sale.
There's frequently this assumption that speculators being involved means gouging, well they will certainly try to gouge people but there's no guarantee they'd be successful. There's certainly a guarantee that buying a group of plane tickets that are refundable will be a profitable strategy since any tickets that can't be sold for a profit will be refunded the original purchase price. However, most tickets are nonrefundable and, as such, this strategy wouldn't work out so well.
Well, if the airlines change their policies, remove restrictions and make the tickets transferable, this would create a whole new market niche for resellers. If this happen there would be many complications related to liability of the resellers, quality guarantees, safety rules and more. It would be virtually impossible for the airlines to operate within the same legal terms, as the do now.
When I read the original questions and then the answer that explains "yield management" or "revenue management" I'd asked myself would I fly on the ticket I bough through an auction website? I would not.
Transfers can be two ways. If they have to register the transfer then of course they should be able to control the flow of cash. HOWEVER, if they don't register it, as for example might the situation if I gave you my bus ticket then, apart from the economic factors, there are clearly a few accountability and safety factors.
If the plane crashes for some reason, the airline would not be in a position to state who was on board. So they would then end up reporting that the ticket seller/donor had died, when in fact it was the recipient.
If the plane is hijacked, or even brought down by terrorists, it could be that the terrorists were the ones who bought the re-sold ticket. And the airline would think it was the original buyer.
Ditto for the situation where someone might have been smuggling drugs or other contraband.
I'm sure you can come up with other safety and security aspects if you think hard enough.
