As people have said, it is due to ratings. I wouldn't say it wasn't profitable, it wasn't as profitable as replacing it with another show. This happens a lot in network television and many shows never come back. Rock Lee spin off replaced the time slot and may have made more money, I do not know what is in that time slot currently. However, Naruto is coming to a close in the next year, it will be interesting to see what show takes Naruto's spot. Will it be Bleach, doubt it, but they will need to replace it with a high profile show as that time slot has made TV Tokyo a lot of money via Naruto. If they do it right, they can advertise that bleach will be taking that slot after naruto and they may get many more viewers if they do it that way. More people will be likely to watch it if it is in that time slot. Like I said, IDK, but it will be interesting to know what takes over because it had a reputation to uphold when it does.