Exactly, even when you add in the transfer fee proposed here. Any rational ticket holder wouldn't sell their ticket for less than [what they paid for it] + [the transfer fee], and that means the airline let someone else get money they could have got if they had just sold the ticket directly to the second person.
The only scenario where this would be useful is if the the original purchaser is willing to sell their ticket at a loss for some reason, e.g. if they know they can't make it and just need to minimize their losses. But at least Southwest airlines already has a customer-friendly solution here, they will credit you the full price of the ticket for a future flight, for most tickets at least.
Original purchasers sell their tickets at a loss back to the airline all the time (for credit). It's called canceling your flight because your plans change for some reason.
As you point out, Southwest lets you do this for free. And JetBlue is something pretty reasonable as I recall. Unfortunately most of the fee-addicted airlines have really ratcheted up their cancellation fee however.
The only scenario where this would be useful is if the the original purchaser is willing to sell their ticket at a loss for some reason, e.g. if they know they can't make it and just need to minimize their losses. But at least Southwest airlines already has a customer-friendly solution here, they will credit you the full price of the ticket for a future flight, for most tickets at least.