“Playing hooky” is more about a particular “episode” of non-attendance, though. A regular person, who otherwise enjoys attending school, can “play hooky” because e.g. they want to stay home to play a newly-released video game. Futoko is—from my understanding—meant more as a sort of constitutional property. It’s something these children are, rather than something they’re doing.

It’s like the difference between “being depressed” and “suffering from depression.” One is a mood, that could be brought about by any number of temporary environmental factors, and really isn’t a “problem” so much as an often-expected reaction that will sort itself out. The other is a long-term state of being with complex etiology that isn’t expected to resolve without diagnosis and treatment.