Hair length depends on so many factors, including facial structure, hair texture and lifestyle. Long hair aesthetically doesn't compliment every woman on the basis of the type of face and hair she has. Furthermore, a person who works out daily probably would not have long hair for the sake of practicality.
I for one have fine thin hair, and an oblong face shape. Long hair past the shoulders weighs down my facial features, and begins to look limp. I achieve a more vibrant, youthful and attractive look with shorter, layered hair. I also work out, and so dealing with reams of hair just won't work for me. Last, I deal with kids all day as a teacher. I need for my hair to look attractive and professional, and be easy to manage without having to primp and play with it. I simply don't have time to do that. Heck, there are days when I don't even get to the bathroom! That's bad, I know.
Anyway, some things to consider.