I don't really understand Roam, although it is favorably mentioned here frequently. I tried a couple of videos but quit after 15 minutes when all they've demod is linking between notes. It seems like watered down NoteCards, with a (really) nice UI. Everyone here is probably familiar with NoteCards but if not, the first two linked papers are very good. https://en.wikipedia.org/wiki/NoteCards

you just gave a few reasons: notecards is no longer available afaict, and roam has a nice UI, so if you want to write notes with links between them, you may as well use roam, no? 🙂

I guess. It's just that at $165/$500 per-year depending on the plan, I assumed I had to be missing something.

ah, per year

I switched off from roam long time ago, so I can't say what they have now, but the killer features at the time were non-hierarchical note taking, easy linking, and backlinks. That's a good way to create a personal knowledge base and that's what most people did. I looked around at that time, but there were little alternatives that offered these features (or they weren't widely known). I know they have 3rd-party plugins now and people do some interesting stuff with them. That's another reason I see Roam mentioned here. Also, Roam used to be free until this summer. Roam introduced me to Zettelkasten which is a great method for maintaining a knowledge base. So if you want a knowledge base, my recommendation for most people is to learn Zettelkasten (How to Take Smart Notes by Sönke Ahrens is a great book) then pick a simple markdown editor with links (zettlr or obsidian.md seem to be good. if you're into Emacs, use org+org-roam). i.e. you don't need roam for that.