Why did Singapore casinos sue Hong Kong and Hui Ling to Hong Kong instead of the mainland?

Hello! China mainland law does not accept cases of gambling arrears or gambling loans, and casinos can only make judgments through Hong Kong courts, and then entrust mainland courts to execute them through Hong Kong courts. According to a document issued by the Supreme Law more than ten years ago, entitled "Arrangement of the Supreme People's Court on Mutual Recognition and Enforcement of Judgments in Civil and Commercial Cases under the Jurisdiction of the Parties by Agreement", the parties may apply to the People's Court of the Mainland or the Court of the Hong Kong Special Administrative Region for recognition and enforcement according to this arrangement. In layman's terms, it is judged by a Hong Kong court and can be enforced by a mainland court. Thanks for reading!