You would see the bigger airlines scooping up everything then. For example, I have several hundred million dollars in cash right now sitting unused. If I was interested in expanding, which I am, I might be inclined to buy up every available plane of a particular type to open the new base. In that situation, someone like you, who doesn't have huge cash reserves, ends up being handicapped because I have the resources to buy everything out there. Now multiply that problem by all the huge airlines in this game world, and the used plane market quickly disappears. (And this doesn't even deal with unscrupulous players who might buy up everything just to limit competition).