Because Chinese is written in ideograms (hanzi) while English is written in phonetic symbols (Latin alphabet). Each Chinese character represents an idea – a noun, an adjective, a verb, a concept, a relation – while each letter represents a sound. The hanzi are basically hieroglyphs – and this is why we can read Egyptian texts from 5000 years ago.
Since each hanzi represents an idea, you do not need to have a faintest idea how it is pronounced and how to say it aloud. This is the beauty of the hanzi – you can read 2000 year old texts without having any idea how it has sounded. And this is also the pitfall of the hanzi – they do not bear the sound, the phonetic value. You do not learn to speak Chinese by knowing the hanzi.
The English-speakers can read English texts only up to 500 years old because the language has changed. The English orthography represents English how it was phonetically written in the 14th century. And if you try to read English phonetically, nobody will understand. You may blame the Great Vowel Shift from making Medieval English incomprehensible for the Modern reader. If English was written in hanzi instead of alphabet, 500+ year old texts would be crystal clear by their meaning for a modern reader.
And here is the twist: the Chinese reader would not have the faintest idea how to read the text aloud in Classical Chinese, as the hanzi do not bear any pronunciation guide. Like Englis, the Chinese language has also changed. A Chinese reader would only comprehed the meaning of the words, not the words themselves. It would be like reading Japanese for him. To really comprehend Classical Chinese, he would need to study it. Conversely, anyone who knows the Latin alphabet can read aloud 2000+ year old Latin texts without having the faintest idea on what it means, as the alphabet bears the phonetic values of the phonemes they represent.
I mean, you can read aloud Quidquid Latine dictum sit, altum videtur, and Marcus Tullius Cicero (I mean /ki’kero:/, not /ˈsɪsəroʊ/) would understand what it means, even if you don’t.