Once your hair starts hitting your shoulders, it hits all your clothes too. So there is more abrasion and your hair can wear and break off. This happened to me - never got any kind of split ends until my hair got shoulder length while wearing all kinds of wool sweaters and coats. Wearing your hair up, or "protective styling" helps prevent your ends from getting damaged.
High Density, High Porosity, Medium Texture, 3B with some kink

Lo-Poo: No Preference
Co-wash: CJ Smoothing Conditioner
RO: CJ Strengthening Conditioner - HG
LI: CK Satin Roots
Styler: CK Coil Jam
Other Likes: Castor Oil; CK Twist Whip, MD CSC
Dislikes: Wheat Protein; Aloe LIs or Stylers