Why do China people in some foreign movies only speak Cantonese?

In areas where there are many overseas Chinese, the first generation of Chinese who entered these areas were mostly Cantonese. With the continuous migration of their descendants year by year, they also brought some cultures from Guangdong to the local area. Local outsiders first came into contact with these Cantonese people, and natural Cantonese is one of them. For example, more and more Chinese restaurants in Guangdong are opening, and some dishes and ingredients on the English menu are transliterated in Cantonese, so foreigners order Cantonese dim sum and cabbage. There are also Cantonese-speaking Hong Kong people. Wushu schools opened in North America in the early years also attracted local foreigners, so Kung Fu and Wing Chun were also transliterated in Cantonese, which had a greater influence until Bruce Lee appeared.

Like Xianggang, Ou Man, which the landlord said, is mainly in Cantonese.