Upgrades to premium cabin, either economy, business, or first is a product that airlines offer to reward its members of their frequent flyer program or those that pay for it. No status + not willing to pay = no upgrade. Its a simple formula. Try to concentrate your flying with a particular carrier, achieve status, and you will start seeing different service. The higher the status, the better the service overall.

There are others that do not have a preference of airlines, free agents so to speak. They buy tickets based on convenience to them and pay for what they want.