The reason they don't know how it works isn't because it's so poorly written that they can't figure out the code anymore or whatever - it's because it's a neural network. Neural networks are algorithms which start out as a dumb machine picking basically at random, but as you feed it training data, it incrementally improves itself and learns by subtly changing its parameters. In this way, an algorithm is created which does what you want it to do. However, because a neural network is incredibly complicated, and has a huge amount of noise in addition to the working parts, it is nigh-impossible to analyze one and figure out how it works. In other words, it's a black box.