So the reason some kids seem to read with some instruction, even if it's not formal and super explicit, is that they have a good phonemic system. That is, they quickly understand that words are made up of smaller units (e.g. cat is /k/ + /a/ + /t/) and can manipulate them without much trouble. That ability is essential to map words efficiently in long term memory for effortlessly retrieval, which in turns creates a sight vocabulary (a large bank of words that are instantly recognized).

Kids with phonemic deficits, on the other hand, cannot efficiently develop a sight vocabulary. Even if they are taught phonics and can decode, that decoding is effortful and leaves little room for more complex tasks.