You may have noticed that English words have a lot of syllables - too many, in fact. Chinese words or composed of more compact syllables and fewer of them. Thus, in English, it takes more effort to say every single syllable, so the natural reaction is to drop some. If you grow up listening to this spoken English, you automatically fill in the extra letters in your mind.
As a result, spoken English leaks vowels and sometimes syllables like a bucket with holes leaks water.
Only people speaking formally in public try to get all the syllables and vowels, because it is more important to be clear.
In some dialects, it gets very bad. You might hear "skwout!" and wonder what that could possibly mean. In some dialects, both British and American, "skwout" means "let's go out".