I can really only answer the first question, since I'm not terribly familiar with the exact specifics of the Sudanese pyramids.

Pyramids have been built all over the world, but the reason the Egyptian pyramids initially gained attention is almost certainly one of scale. While Nubia has more pyramids than Egypt, they were built far later than Egypt and are far smaller. Here is a page that gives some examples of some Nubian Pyramid setups. The tallest of the three is only 50m high, where the great Pyramid was nearly three times that. The Egyptian pyramids have a much lower slope (think 40 to 50 degrees), meaning they have a much wider base, making them both far taller and far larger than the Nubian pyramids.

The Egyptian pyramids are some of the ancient world's largest constructions, and the great pyramid itself was the tallest known building for several millennia. While Sudan has more known pyramids, the pyramids they do have are smaller, more recent, and as far as I'm aware, were all raided before modern times.

There are about 200 egyptian pyramids about 2000 Kushite (upper Sudan today). The Egyptian pyramids were much older, much bigger (Kufu's was the biggest man made structure until the Cathedral of Cologne was built) and on a whole other scale.

the Kushite ones show the relationship between the Egyptians and African civs. bilateral trade, movement of ppls, movement of knowledge back and forth.

Kushite kingdoms were overrun by various wars with new peoples. Meroe, Nubia, and the pyramids would have been raided whenever instability happened (it tells everyone where the good stuff is buried. like robbing banks because that's where the money is)

the egyptian ones get more attention because of the conquest of egypt by greece, rome and then britain. whereas the upper Nile remained outside direct contact with the Med. Sea and then got cut off completely by the Islamic conquests of the 600s.

Much of African contact simply got forgotten by the Middle Ages. The portugese were stunned to run into black Christians in Ethiopia. And Israel in the 1970s/1980s had a hard time (and still does) of accepting the existence of African Jews (Ethiopian jews make 40% less in a recent study). East African civs simply fell off the map even though they were as old as Egypt/Mesopotamia and (as the pyramids show) as developed.

I think it's mostly due to the fact that the Egyptian pyramids are far older and much bigger. They're some of the most astonishing things we have from the ancient world, which makes them far more "important" than any other form of pyramids. Just compare the Egyptian ones with the Nubian/Sudanese, it's not so weird that the Egyptian ones cause more attention.

Sudan was a part of ancient Egypt and therefore Egypt had a large cultural and geographic influence over the region. The Nubian pyramids were built by some of the leaders over the Kingdom of Kush as a tribute to the cult of the Egyptian god Amon. If this was the only content of the pyramids I don't know, but it's the only facts I'm sure about.