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.