Why Hong Kong people can't speak Mandarin very well, but Taiwan Province people can speak it very well? Why?

Geographically speaking, Hong Kong is actually a part of Guangdong. Most of the indigenous inhabitants of Hong Kong are Cantonese, while the indigenous inhabitants of Taiwan Province Province are mainly composed of three parts: 1, brought by veterans; Mainland immigrants, mainly Fujian people; There are also the indigenous Gaoshan people in Taiwan Province Province, accounting for only a small part. Therefore, the official language of Taiwan Province Province is Mandarin with a southern accent, and many people can speak Minnan.