Here's why:
* Mandarin is the official language of China, but it is only spoken by a majority of the population, not everyone.
* China has many other languages and dialects, including Cantonese, Wu, Min, Hakka, and many more.
* Some dialects are mutually unintelligible, meaning speakers of different dialects cannot understand each other.
Think of it like this: Imagine if you were to travel across different countries in Europe. While most people might speak English, many also speak their own local languages, and they might not understand each other.
So, while Mandarin is the most widely spoken language in China, it's not the only one, and many Chinese people speak other languages and dialects.