The literal ground doesn't have the same potential everywhere. This is obvious in case of lightning strikes, but also happens in normal circumstances. You as a human standing on the ground are mostly at ground potential. If neutral was connected to ground at the nearest substation or the next power plant but not at your home you would get an electric shock whenever you touch a neutral wire because of the difference in ground potentials.

Neutral can also be connected to a neutral line on the grid. But you pretty much always want to connect it to the local ground through a literal metal post.