Question

Why does geostationary satellites always have to be on the equator??

Answer 1

Because that is the only way to remain above one spot on the Earth.
Geostationary satelites remains in the same position above earth all the time.Means it's over the equator.And it has rotating speed that equals to the earth.Thats how it reamins in the same position.
If it not on the equator,even if having same of earth,it can't stay in the same position(due to the shape of earth).