Why is the ocean not flat?

Answer 1

Do you mean the surface of the ocean or the ocean floor?

Waves, which dominate the surface of the ocean, are generated by atmospheric winds that transfer their energy to the upper layers of the ocean. The weather which generates these winds is driven by differential heating of different portions of the earth, which creates area of low and high pressure. Areas of differential heating are reinforced as upper latitudes receive less solar energy than lower latitudes leading to consistent presence of areas of high and low pressure, and thus consistent winds and consistent waves.

The ocean floor is not flat as tectonic forces drive oceanic plates apart from each other and into continental plates. Areas where ocean plates are being spread apart results in mid-ocean ridges and occasionally result in islands that emerge to the surface e.g. Iceland. Areas where oceanic plates hit continental plates are called 'subduction zones.' These subduction zones contain deep ocean trenches where the lowest points on the surface of the earth are located. These subduction zones are also where some of the world's largest earthquakes occur.

Hope this answers your question!

Answer 2

the earths gravitational pull