I think you’ve covered it all here but I’ll add my slightly different use case to your list

I use iPod Classics, I haven’t tried rockboxing any, though. I’ve been meaning to but haven’t yet.

Many artists I like aren’t on all (or any) of the streaming platforms. I also still buy CDs and generally like owning my copies as much as I can.

I hate user interface changes/companies like Spotify having the ability to disable basic features on a whim

No internet, buy once/no ads/no drm, and no touchscreen are important to me. The click wheel is just so good lol