Writing is just a proxy for speaking. And entirely its own thing. Think about Greek. There are ancient texts from thousands of years ago that would be kinda weird but basically legible for modern readers. However, same text read in ancient pronunciation would be unintelligible. Search for Shakespeare in historical accent. Then suddenly a ton of things that seem weird in modern English actually start to rhyme and even make funny homophones jokes.

Essentially, written word is a living system. Learning this system is not just about its internal logic, but learning about its history and the myriad of quirks it picked up along the way.