It's similar to people building their own computer rigs. I built my own computers when I was younger and broke. It was cheaper to buy the parts and do the build yourself than it was to buy an off the shelf solution. It's also a great way to learn about the computer. As I got older, I would still lean toward building computers. However, today, I have way more responsibilities to be building the hardware, and my time is way too valuable to care about doing that myself. I just need the damn thing to work, and when it doesn't, there's a person to contact about resolving the situation. Between work, family, hobbies, etc, I have chosen to no longer care about these customizations/tweaks. There's really nothing different today for me to learn about a computer by doing the build myself: cpu, ram, bus, i/o controllers, etc. The core fundamentals are the same, just tech and speed has changed. My current devices have stock backgrounds. Rarely do I see my desktop as I have too many windows open doing actual work.
TL;DR I too care much less about this, but understand why others do. I encourage them to keep doing it even if I don't personally spend time with it.
I still build my own PC's even though on a similar cost/benefit basis it would make sense not to perhaps.
Thing is I build PC's for both gaming and software development and frankly for that goal the delta between build it yourself and someone else building just on price is pretty large but there is also the fact that if I build it myself I know exactly which parts are in there.
TL;DR I too care much less about this, but understand why others do. I encourage them to keep doing it even if I don't personally spend time with it.