There are many reasons, but the BIGGEST one, is that professional photographers know how to make women (and men) look their best! The way photographers do that, is mainly by choosing the angle of light that is falling on people's face. The angle of light can make wrinkles to softened or to make them stand out (we only see wrinkles because of the shadow they create)
The type of light. When photographing outdoors, the time of the day when photos are taken is the type of light that will either enhance the photos or ruin them. The light in the middle of the morning is harsh and the shadows it creates are deeper while the light in late afternoon or evening is softer and it has the beautiful golden tone that everybody loves.
Choosing the right light is the first step for a great portrait!