I know that. It is the same here in Taiwan. Around Taipei, most people speak Mandarin.But you go to some of the southern parts and ( mostly with the older folks- my inlaws and such ) they speak mostly Taiwanese, even though Mandarin is the "official" language. You even have Hakka spoken in some parts.
Of course Hakka is spoken in some parts ~ it’s the only way you can communicate with the coastal Chinese communities throughout the disaspora into the Indonesian archipelago and other Southeast Asian places for one thing. Plus, their food is better.