I wouldn't call it a stigma. I'd say there are issues with doing it appropriately. Adults have jobs, children, etc. They do not have the same "freedoms" a child

I wouldn't call it a stigma. I'd say there are issues with doing it appropriately. Adults have jobs, children, etc. They do not have the same "freedoms" a child has. While a child is forced to learn because of school+family, they have "free time" that is used to reinforce that. With adults, "free time" for reinforcement is harder to allocate.