In Alien Resurrection, the crew are afraid of returning to Earth? Why, what has happened on Earth?

In the film, Johner says, "Earth? I'm not going to that fucking slum."

A deleted final scene actually shows us the state of the planet - and it doesn't look pretty. It would appear that a cataclysmic event has left the planet a barren wasteland.

I, too, would be reluctant to return to Earth.

Deleted Scene from Alien Resurrection