DIY is only worth it if you enjoy building PCs as a hobby or if your funds are very limited.
... or:
- if you want something with exactly the (premium or non-standard) components you like or require
- have great expandabilities inside your computer, without having to resort to external "dongles" everywhere, because your PC is either build too small, has too few PCIe slots to your likings, or is non expandable at all internally.
- don't want to deal with cleaning up systems that come pre-installed with garbage gallores of bloat-, mal-, or nagware
i personally don't build my PCs anymore since i'm basically notebook only for the last 20 years, but i don't get the notion that building your PC is something negative to avoid. you only have to do it once for maybe half an hour or so, but you're getting getting everything exactly as you like.
i'm still building my bikes though (from pre-build components), so i'm not welding my own frames. i'm paying more this way, but in exchange i'm actually getting exactly the components and the frame geometry that i want.
not something compromised because someone thought that that certain set of parts will fit everyone, or that most people won't care anyway.