Some do learn to read (I've heard numbers from 5-15%) but they read like speed readers going straight from a string of graphemes directly to meaning without translating to phonemes. You may be underestimating the difficulty. It would be like trying to learn to speed read Arabic without ever having heard it spoken. And it's not like they generally don't try; most profoundly deaf people can read "2 apple for $1" or "Caution" or "Restroom" but that's not literacy.
Some do learn to read (I've heard numbers from 5-15%) but they read like speed readers going straight from a string of graphemes directly to meaning without translating to phonemes. You may be underestimating the difficulty. It would be like trying to learn to speed read Arabic without ever having heard it spoken. And it's not like they generally don't try; most profoundly deaf people can read "2 apple for $1" or "Caution" or "Restroom" but that's not literacy.