Why can people from Meizhou and Ganzhou communicate with each other?

Because the two places speak the same language, Hakka.

To talk about Hakka, I have to explain to you what Hakka is. The Hakka people were born during the chaos in China at the end of the Eastern Jin Dynasty. The ethnic minorities in the north massacred the Han people. Many people fled to the south to avoid the chaos. Because they migrated from other places, they were called Hakka people. At that time, the south was sparsely populated and a barbaric land. The arrival of the Hakka people led to great development in the south. Meizhou and Ganzhou are two major Hakka gathering areas, and they are also transfer stations for Hakkas to move to other places! Today's Hakka people are mainly distributed in southern Jiangxi, eastern Guangdong, and western Fujian. From the map, you can see that these places are all connected together. Meizhou and Ganzhou are the main places where Hakka people live, and most of the current residents are Hakka people. Ganzhou is also known as the Hakka capital. Nowadays, Hakka people are spread all over the world. Hakka people are also very business-minded and are known as "Oriental Jews".

The Hakka people speak a unique dialect - Hakka! In fact, it is not accurate to say that it is a dialect. Hakka actually evolved from the language brought to the south from the Central Plains during the Jin Dynasty, and it retains many pure ancient pronunciations.

For example: the stone path of Hanshan Mountain in the distance is "Xie" (pronounced with the second tone of xia). The pronunciation of "Xie" in Hakka today is still the same as in ancient times. The Mandarin we speak now, that is, Beijing dialect, is greatly influenced by Manchu. Hakka is the authentic ancient Chinese language.

Sorry, having said so much, I am a bit off topic. In short, the Hakka people in Ganzhou and Meizhou speak Hakka, so they can communicate with each other.