Here's why:

* Earth is destroyed in the original Mass Effect. The Reapers, the main antagonists of the series, raze Earth to the ground in the opening moments of the game.

* No rebuilding effort is depicted. While there are some references to the destruction of Earth and the loss of life, the games focus on the larger galactic conflict and don't explore the rebuilding of Earth in detail.

* The focus is on the galaxy, not Earth. The Mass Effect games are about the struggle against the Reapers, exploration of the galaxy, and interspecies relationships. The destruction of Earth is a significant plot point, but the focus is on how this event shapes the galaxy's future.

So, while Earth plays a role in the Mass Effect story, you won't be able to visit it or see its remains in the game.