Because ours is real Canto.
Kecian ts

I know HK follow Chinese script. Well... obviously. Their Cantonese words have direct a counterpart in Mandarin, like 你, is 'ni' in Mandarin and 'nei' in Cantonese. But our Cantonese, we say lei. Why are we so different?

Another example:

的
Mandarin: De
HK: Dik
Local: Gei

对
Mandarin: Dui
HK: Deoi
Local: Ngam
UPDATE:

Apparently I am wrong as pointed out by a ktard. These words have a direct counterpart in Mandarin, see answer 5.
的 is Dik
嘅 is Ge (correct)

对Is Duii
啱 is ngam (correct)
/K answers as simplied below:

1. Influenced by other dialects

2. The words we use are slangs, which HK also use. But we don't know the formal words, which HK knows and use

3. These are 'Lazy' pronunciation, as the language evolved.

4. KL more different from Hongkie. But Ipoh/Sabah closer to HK

5. The 'slangs' are actually found in Mandarin words. It is just that they are rarely used in Mandarin but have more meaning in Canto.
Additional info on corrupted Malaysian Cantonese:

http://www.usj.com.my/bulletin/upload/show...se-is-corrupted]http://www.usj.com.my/bulletin/upload/show...se-is-corrupted

https://chineselanguage.org/forums/viewtopic.php?f=2&t=654

Because ours is mixed with Malay + english compared to theirs that mixed with mandarin.

Example, I say mata (police) but they call it geng-chat. Some that mixed more with mandarin speaking wont call Jing-cha, and Gong-an, or Gong-On. (same like security guard. We call seh-kiu, they called it bou-on)

We call money Lui, they call it Chin. We call pineapple Wong-Lai, but they called it Boh-Lo.

Just somewhat different from translation. As long can campur can d. Even soy sauce also. We call See-Yau, they call Sang-Chau, or Jiong-Yao.