If all you want to do is to generate a texture by looping over all pixels in sequence, then yes, you can use a RNG. But in many use cases you need to evaluate a

If all you want to do is to generate a texture by looping over all pixels in sequence, then yes, you can use a RNG. But in many use cases you need to evaluate a noise function at an arbitrary (x, y) position (or (x, y, z) or even higher dimension) which means you need to hash the coordinates to get the pseudorandomness you want.