That's because the air flows in slightly different ways at different speeds and at different altitudes. In general, low to medium speed airplanes have airfoils with more thickness and camber. Because the airplane is not moving through the air very fast the wing needs to generate as much lift as possible at a slower speed. The air density at lower altitudes is greater. More molecules in the air generate more lift than fewer molecules in the same amount of air.
Greater camber gives greater lift at slower speeds.
That's because when flying close to or at the speed of sound a shock wave forms at the nose of the airplane. NASA researchers discovered that a thin airfoil delays the formation of the shock wave. This reduces drag that is caused as the airplane moves through the shock wave. Their investigations gave results that are still used today to influence the design of new aircraft. Wings provide the majority of the lift for an airplane, but wings also cause drag.