Here's why:
* Hair texture is determined by the shape of the hair follicle. The shape of your hair follicle is genetically determined and cannot be changed by shaving.
* Shaving only removes the hair shaft, not the follicle. The hair follicle is the part that creates the hair, so shaving does not alter its shape.
* Hair will grow back with the same texture. When hair grows back, it will have the same curl pattern as it did before you shaved it.
However, shaving can sometimes *appear* to make your hair straighter. This is because the freshly shaved hair is very short, making it less noticeable if it's curly. As the hair grows longer, the curls will become more apparent again.