bc the diamondshaped earth provides gravity.
The gravity exists bc the earth is spinning so fast that you don´t even notice it at all.
Since the earth is a solid obstacle it keeps its shape and thus it stays a diamond.
Please explain me this part. If the earth was a diamond, gravity would even out the surface to a (near) globe and the spinning would cause the equator to be slightly off the globe. That would result in an ellisiod, which is what the Earth is right now.