Why don't all airplanes have winglets?

ICAO Annex 14 groups aircraft according to wingspan and landing gear span into 6 groups labeled A-F. Moving into a higher size class will reduce the number of gates and the taxiways the aircraft is allowed to use. read more

Winglets create a lot of stress on the wing, and when you take the mission profile of the plane compared to the fuel economy winglets are supposed to deliver and the cost to have them installed (even on new airplanes), they do not add up for short flights or lower altitude flights (ie: on turboprops). read more

But in many instances, airplane makers simply don't have the option of making the wings longer. For example, narrow-body airliners such as the Boeing 737 and 757 often operate from gates at airports designed for short- to medium-range domestic flights. read more

Smaller planes are generally designed to have much lower air speeds, so have a wider wing without much (if any) taper as it approaches the tip. While the spill over still occurs, the different wing shape makes the loss of lift at the tip less critical. read more