question about why people expand their palate

[iamnotgrayipromise]

why do people actively try to expand it with MSE and stuff like that, even if your upper jaw expands, what happens to the lower jaw? even if possible and only your upper jaw expands, you ruin your bizygomatic to bigonial ratio. how would it expand along with the lower jaw if no force is being applied to it. it stretches the upper jaw horizontally no? so do you end up with a flatter profile?