I’m pretty sure we’ll find out as the story keeps going. I can only imagine it was because he wanted to stay in a world where he would eventually meet with yashiro again but it could certainly have a different reason.
if he remains in the yakuza world then he will meet Yashiro again since he's run a casino and casinos sometimes have underworld people. This is what I understand.
Why did doumeki keep being a yakuza after he was thrown out by yashiro?