Why do things that enter a black hole disappear?
The gravitational attraction of a black hole is extraordinarily large, it is so strong that light itself cannot escape. Once any particle passes the event horizon it will not escape the black hole.
The reason we see things is because light reflects off an object and travels to your eyes, if light cannot travel away from the black hole because of gravity then that light can never reach your eyes and so all you see is black (no light)!
So you will see an object approach a black hole but once it passes the event horizon you will no longer see the object.