It's a warehouse job that demands real physical labour each day of course people leave if they get a better offer or even a worse offer that requires less work.
It's also a job that will be there until it can be automated or until Amazon closes, and I think it's the latter that's the closest to happening. Until that happens, it'd be better for everyone involved if the tasks that need doing can be arranged so that long-term employment is viable. A job shouldn't be as exploitative as it can be just because there will be someone who's in a rough enough spot in their life that they will take it.