The primary reason why black women tend not to have long hair is because it can be difficult to retain. The hair grows just as quickly as it does for women with straight hair, it's just that kinky hair can be dry and more prone to breakage. If the hair is breaking off a 1/2" every month, and grows 1/2" each month, there will be no addition to the hair's length.
Protective styling is important because doing so keeps the end of the hair moist, protected and less available to things that cause breakage (friction against your collar or dry air). Protective styles also allow for less manipulation of the hair. When you twirl your hair or comb and brush it all the time your hair is more likely to fray and snap off. If your hair is in a protective style, you can go for days and weeks without having to stress your hair by manipulating it.
The most popular ideas for protective styles are braids and twists, with or without extensions. They can last for an extended period of time, giving your hair a rest. Just remember to continue to moisturize your hair while the hair is braided or twisted or your protective style may work against you. Also, if hair is added, make sure that the fake hair is not braided in too tightly, to avoid breakage from the pulling.
Comb coils may be an option for shorter hair.
If your hair is long enough you can take your twists and put them into a bun for extra protection or you could even do a bun on loose hair to protect it from the elements.