Scribbly near the end usually just means ran out of time before the printer's deadline, rather than, say, a degenerative nerve disorder. Now. consistently missing deadlines is probably cause for concern, but people have other time commitments.
Like, I recently read that the reason Sonoda Kenichi -- the guy who did Riding Bean and Gunsmith Cats back in the '90s and early '00s -- isn't doing as much manga/anime work these days because he had to go back to Kumamoto to take over running his family's candy shop/factory (which has been making chōsen-ame since 1582). So you never know. (Not sure how much you want the guy who wrote/drew Minnie-May Hopkins hanging around a candy store, but there you go.)