Because there aren't any jobs available in their field?

If you want a roof over your head and food on the table, maybe you have to take a job outside your field.

Working at a job outside your field doesn't mean you can't keep looking for work in your field.  And when you find something in your field, not having to explain a gap in your resume might help you land that job.

Oh, and working at a job you can do in another field might introduce you to another field you really enjoy--and might not have considered before.