Some possibilities:
- UI : IMO the UI of default tiddlywiki is less appealing than the more mainstream Knowledge Base Software. Obsidian has a graph view that is very appealing, Logseq too + the UI is minimalist. Roam look like a simple bullet list (and provide a graph view, like the others). The home page of the official website could be redesigned to be less dense - all the other website have their download button immediately visible, and much less text. Tiddlywiki.com display a lot of thumbnails leading to guides to introduce itself which could be a bit overwhelming.
- Ease of use : Tiddlywiki require a browser extension or to download tiddlydesktop or similar (which the user need to search for and find on the website), while the other software are usable out of the box. Sure, you can use the default build-in saver but mainstream users wont bother with that. The simple fact that the user has to choose between a lot of options for a saving method can be offputing, especially if you have no technical knowledge. IMO tiddlywiki should provide ONE recommended saving method, and offers others solutions as an option. This : “There’s a wide variety of methods available, with different features and limitations” is not a good thing to say to someone easily overwhelmed
- Lack of publicity : Not enough video/articles on tiddlywiki, like you said
- Steep learning curve : wikitext, filter expressions, widgets are not easy to understand for people that are not programmer.
- Scaling/Performances : tiddlywiki performances decreases quickly when the file get big, which can happen very easily if an user try to import images into their tiddlywiki rather than using external embedding. It’s not possible to search across multiple wiki either (at least not without addons) - it would be easy to think that tiddlywiki is not cut out for the task. Maybe a build-in tutorial (addon ?) could help mitigate those two last issues.