Why earth rotates only from west to east?

The angular momemtum of pretty much the whole solar system is in that direction. All the planets revolve that way, the sun rotates that way, and almost all of the planets rotate that way. Venus is the odd exception, and it rotates backward, but very slowly. The primordial stuff that eventually coalesced into the solar system was on average moving that way when it started, so that's the way it rotates still.