Why didn't egypt invade nubia during the classical karma period

Terrian prevented it, as well as Egypt had little to gain from invading

Nubia is a region along the Nile rivers encompassing the areas between what is today central Sudan and southern Egypt. It was the seat of one of the earliest civilizations of ancient Africa, with a history that can be traced from at least 2000 B. C. onward, and was home to one of the African empires. There was a number of large Nubian kingdoms throughout the Postclassical Era, the last of which collapsed in 1504, when Nubia became divided between Egypt and the Sennar sultanate, resulting in the Arabization of much of the Nubian population. Nubia was again united within Ottoman Egypt in the 19th century, and within the Kingdom of Egypt from 1899 to 1956.