Before relaxers became easily accesible,black people straightened their hair,through a variety of means,many of which were very harsh and demaging.
Black hair in it's natural state has a tendency to shrink up,preventing you from seeing it's real length,leading to the popular belief that it doesn't grow long.
Hair grows an average of 1/2 inch per month,including black hair.your black hair is growing,but you may not be retaining the length due to chemical abuse,dryness,excessive heat stying and a general lack of proper care.
Many product you'll find in the ethnic hair care section of your local stores are full of ingredients that aren't the best for black hair.please take note.'Petroleum and mineral oil'make up a large percentage of black hair products and all they do is clog your scalp and attract dirt to your hair.A better approach is to apply natural oils directed to your hair,paying special attention to the ends,which tend to be dirty.
Above are pictures of women with natural hair and still look beautiful.