Here's why:
* Hair Structure: The shape of your hair is determined by the structure of the hair follicle and the bonds within the hair shaft itself (especially disulfide bonds). These are determined by genetics.
* Temporary Stretching: Braiding stretches the hair shaft and can temporarily relax the curl pattern.
* Washing: When you wash your hair, it rehydrates and returns to its natural state. The bonds that give your hair its shape reform, and the temporary stretching from braiding is undone.
* Heat is Needed for Lasting Change: To permanently alter the shape of your hair, you need to break and reform the disulfide bonds using chemical treatments or heat styling.
In summary: Braiding can temporarily smooth and stretch the hair, but it won't permanently straighten it. Your hair will return to its natural texture after washing.