Here's why:
* Pronunciation: The sounds of Mandarin and Cantonese differ significantly. This is especially true for tones, which are crucial in both languages.
* Vocabulary: While there are some shared words, there are also many words that are different or have different meanings.
* Grammar: Some grammatical structures differ between the two languages.
However, there are some important things to note:
* Shared Writing System: Both Mandarin and Cantonese use the same written Chinese characters. This means that someone who can read Mandarin can also read Cantonese.
* Exposure and Context: Cantonese speakers who have lived in areas with significant Mandarin exposure, or who have been exposed to Mandarin media, may understand some basic Mandarin phrases.
* Learning: With effort and practice, people who speak one of these languages can learn to understand the other.
In summary: While Mandarin and Cantonese are both Chinese languages, they are not mutually intelligible. They have significant differences in pronunciation, vocabulary, and grammar. However, shared writing system and exposure can help people understand some basic phrases.