Gravity pulls from all directions. So any shape that is not a sphere will encounter a gravitational pull to shape it into a sphere. There is also the centrifugal force of a spinning Earth, which forces the Earth to bulge slightly at the equator (like a spinning top shape). So that’s how the Earth got its lovely figure 😉
Because this is the most stable shape for a rotating object with large mass (hence large gravitational field) which is able to flow or creep slowly internally.
Comments