For me, it's simply because it's been incredibly easy to swap out broken parts as they come and go. I don't have extreme performance needs with my main machine,

For me, it's simply because it's been incredibly easy to swap out broken parts as they come and go. I don't have extreme performance needs with my main machine, and various spare computer parts always find their way into my life, so it's been very cheap to maintain from the beginning, and I don't have worries about running it into the ground. Laptops and other portables are harder in this regard, especially regarding batteries and intense usage. Other then that, I really don't see how adding keyboard/mouse/screens couldn't do the same thing though really. In fact my plan is to masquerade a laptop as my main desktop computer to save space and use less electricity. It will have no other purpose then to be my "desktop" as I have another laptop better suited for portability and battery life. Built-in power backup for my main rig is a plus though!