...so is partly a matter that these parents are enablers? At one time in my life, I'm sure I'd love to have done nothing but stay alone in my room for months of time sleeping and doing internet stuff, with my meals and such prepared for me and placed by my bedroom door, but there is no way my parents would have allowed that.
Enabling parents are one part of the equation. But hikikomori might just be a cultural variant of Internet fixation. Independent adults are less likely to be called out on their addictions, because no caretaker is watching over them. How did the study find 88 hikikomori? They were reported by their parents or friends.