Why spelling drifted from sound
English spelling is not random. Most of its oddities are a record of how the language used to sound, frozen while the sounds kept moving.
The Great Vowel Shift
Between roughly 1400 and 1700, the long vowels of English moved. The vowel in "bite" was once close to the vowel we now use in "beet"; the vowel in "meet" was close to the one in "mate"; "house" had a vowel like the one in "goose". Over those centuries each long vowel rose in the mouth, and the highest ones became the diphthongs /aɪ/ and /aʊ/.
Spelling had started to settle during the same period, helped by printing after the 1470s. So the letters kept the older picture — which is why the letter i spells /aɪ/ in "bite", and why the same vowel letters mean different things in English than in Spanish, Italian or German.
Silent letters are fossils
The k in "knight" and "knee" and the w in "write" were once spoken. The sounds fell away, mostly by the 1600s, but the spellings stayed. The gh in "night" once stood for a sound like the ch in German "ich" — the same sound, further back in the mouth, is the ch in Scottish "loch".
Letters added on purpose
Some silent letters were never pronounced at all. English borrowed "debt" from French as "dette"; later writers added a b to point to the Latin "debitum". The s in "island" was inserted by analogy with "isle", a different word. These spellings show a word’s history, not its sound.
Layers of borrowing
After 1066, French-speaking scribes brought their own habits: "ou" for the vowel of "house", "qu" for "cw" (Old English "cwēn" became "queen"). Latin and Greek later added spellings like "ph" and "ch" in "photograph" and "chorus". One language, several spelling systems layered on top of each other.
No accent is wrong
Every accent is a consistent system. Speakers who drop the r in "car" do it in every word where r follows a vowel; speakers who say it do so just as consistently. A "standard" accent is a social convention — useful for dictionaries and broadcasts — not a more correct kind of English.