Morrowland is either a penal colony or a settlement for treatment of the mentally ill.
If it's a penal colony, the small island is a kind of punishment: You can't leave anywhere and a place so small gets very boring very fast. If it's a mental facility, it's designed to emulate everyday life without a lot of stress factors. Every inhabitant of the island has one specific defining trait, which might be remnants of what was a mental illness in their old country. Note that the only woman on the island is far beyond her reproductive years and/or was infertile in the first place. That way the managers of the facility don't have to deal with unwanted children. Except for that one time, of course.
The lack of guards and/or nurses is easy to explain: You don't need guards when you don't expect your prisoners to escape. As for the nurses? They left as soon as they found out Morrowland can sustain itself and the inhabitants are happy with where they live.
