Even if I don't share it with anyone it helps me figure stuff out. I don't read back 90% of what I write, the writing itself is what provides most value to me. Although it can be handy to dig into the archives to understand my thinking of months back.
Tooling wise; I like handwriting, as I can draw arrows and quick sketches. I used to always carry an A5 notebook around, now I use an iPad with Apple Pencil (recently upgraded to the new mini which is perfect A5'ish size).
Apps I use on the iPad are; GoodNotes for actual notes and Concepts for more visual sketching and such.
If I need to take notes that I need to share I generally use https://nota.md which is imo by far the best markdown note taking experience available. Think of it as a markdown editor with code editor features (e.g. multi cursor). It also works with normal markdown files so no lock in.
When on my phone I use the Notes app on.
Yes, lots of tools, but I find different tools are best for different things. It does means everything is spread around, but it works for me, it's sort of an organized chaos, I can find stuff when I need to.
I think the joy comes from the idea of maintaining all information, of "getting your shit together" in a way. I think most humans truly enjoy collecting and organizing things. Notes, similarly to todos, bookmarks, lists etc are just tools to scratch that itch, the more the better!