It’s simple. I can understand all the parts. While I also understand all the parts in a computer and can tell you exactly what happens every time you hit a key on the keyboard, most people don’t. They could however have a good guess at how a fountain pen works (or a pencil, but hey, I don’t care about those).
It impresses other people who like shiny things. I’m an egotistic bastard, and I like it when people are jealous of the things I have. A character flaw, but I don’t care.