That is because they are not doing their job:
"If the Yakuza are criminals, why don't the Japanese police simply arrest them?"
https://www.quora.com/If-the-Yakuza-are-criminals-why-dont-t...
"If the Yakuza are criminals, why don't the Japanese police simply arrest them?"
https://www.quora.com/If-the-Yakuza-are-criminals-why-dont-t...
See; While many Yakuza syndicates, notably the Yamaguchi-gumi, officially forbid their members from engaging in drug trafficking, some other Yakuza syndicates, notably the Dojin-kai, are heavily involved in it.