Think the thing to emphasise here is the difference between being "unfit to operate as a crew member" (caused by a number of factors including fatigue) and unfit to travel onboard an aircraft (severe ear pain caused by the common cold/serious inability to control bowel movements etc)
If someone goes sick on their last day of work, it is quite obvious that they will wish to travel home rather than spending several days recuperating alone in a travelodge.
In "civilised" countries, the employer has a duty of care of employees post flight duty. The bean-counters have all but eliminated it, but it still exists in French law for instance, where a road accident due possible fatigue on the way home would be an "accident du travail" (work accident) For this reason a few (very few) good employers (Lufthansa for one I know) offer crew hotels after a long duty period (certainly for Long Haul crew)
Like many other aspects of this job, we have zero respect from fiscally focused little bean counters who sit in an office (during office hours ) & any "respect" we want has to be fought for.