I think of these are people from third-world countries going to first. A visa isn't a sure thing. And I'm pretty sure promo fares don't allow refunds because a visa wasn't obtained.

I think the minority is people on FT who do mileage-runs to places that need visas (Saudi Arabia comes to mind). You don't have much time to book it, but then realize the visa takes forever (and you may not get it).

But yea, I don't understand why you need a ticket. Can't anyone just buy a refundable ticket, and cancel the return?