For the most part, I subscribe to all of the same ideas already mentioned here, as shallow as they are I'm just another man with complexes, vices and vanity.
There's just one thing to add on my end - I don't like the finality that comes with purchasing a complete genuine piece. I think that for me the big allure is the journey; the fact that try as you might, you're always on a trajectory to your goal but rarely arrive at the destination. The destination would probably be an all period-correct, matching genuine parts build, which is ultimately stasis and the end of a project.
The watches we put together are flawed, we have little to no disposable parts to replace the worn or broken ones and we spend time improving, improvising, hunting for information or parts, buying tools and learning new techniques. We connect with tons of cool people in the process and this why many of us are here and this is why this is awesome.