Now for the second question -- why did this project take us so long?
Well, it turns out that taking pictures, and assembling a sequence of images that covers the whole asteroid, is really difficult, for a bunch of reasons.
First of all, Eros has a really funky shape. Different people have described it as a sock, a potato, a peanut with a tumor, and a boomerang. What this means for us is that when the NEAR spacecraft is in orbit, the distantance between it and the surface, as well as the angle of the surface below the spacecraft, is constantly changing. This makes it rather difficult to get a good picture.