Because in real yakuza you can't leave without at least having your fingers chopped off, if not flat out being killed. This ending is actually pretty realistic.
Assuming that the guy who doesn't want him to leave was the leader. Why didn't that guy want him to leave? is one of the many questions I want answered.. A back story could've been helpful like was he bought by the leader?.. bcuz in some yakuza stories you see some of the underlings acc set free
I know he couldn't leave because he's part of a gang but I wish there was more explanation to it not just he couldn't leave bcuz he's yakuza..
I wish there was more explanation on why he couldn't leave..