Yeah, it's one of those social issues that I don't really get, since the society I grew in doesn't handle issues in such a roundabout way. A shut-in is more likely to be taken to therapy, and his or her parents are a lot less likely to actively help them stay in their rooms 24/7, and might even go the extreme route of dragging them out by force.
It's still kind of weird since Japanese society is a lot more demanding of people in terms of academics, social relationships, work philosophy, and yet there can be situations where a son or daughter is somehow allowed to cut all ties with the outside world while the rest of the family either looks the other way or actively supports that behavior rather than actively trying to help them get back on their feet.