There are definitely people who want more than that. Some controls I am always looking for in a UI library before I even think about using it is a more advanced

There are definitely people who want more than that. Some controls I am always looking for in a UI library before I even think about using it is a more advanced list control (or table view) which supports columns, sorting etc., and a "tree view". Of course, as the GP wrote, it's hard to implement these without getting more opinionated. Plus, I might add, it's also hard to do these while staying "mobile-friendly".