After building like eight personal wikis/information management systems/hypertext databases (and becoming exceedingly efficient at it) I'll say the problem is that 99% of their uses decompose into three disjoint usecases:

1. Todo list+journal
2. Learning
3. Reference archive Roam-style things let you write simple todo lists (just a list with checkboxes) to organize your day. But todo list apps can provide more domain-specific functionality, like scheduling, reminders, habits, etc.

“A Persian miniature of the cosmic microwave background, from Herat circa 1600, trending on ArtStation” “A universe made of Wang tiles in the style of M. C. Escher, trending on ArtStation”