With ChatGPT why are autocorrect and spellcheckers still bad?

Apple autocorrect and spellchecking is still absolutely terrible and the majority of the time incorrect. If ChatGPT can correctly parse my complex sentences and paragraphs why can’t Apple and Google for that matter (Google you are more on the hook) get spelling and autocorrect functionality right? Autocorrect on my iPhone is absolute garbage for the most part.