What prevents the bittering family from returning to earth?

The Bittering family is prevented from returning to Earth primarily due to the drastic changes in the environment on Mars, which make survival on the planet increasingly difficult. Over time, they become more acclimated to their new surroundings, both physically and psychologically, leading to a sense of alienation from their former life on Earth. Additionally, their growing adaptation to Martian life and the influence of the planet's conditions contribute to their eventual decision to abandon any thoughts of returning.