In "The Metamorphosis," what is Gregor's role in the family and why does he have so much responsibility?

We are told that
Gregor has the job of working as a travelling salesman so that he can support the rest of his
family, his parents and his sister, who do not work. Thus his job is incredibly important to all
of their well-being, which perhaps explains how upset and concerned his parents and Grete are
when he is unable to get himself out of...