It's not about hierarchy or flexibility, but the ill-defined nature of what 'notes' are. Ask people to share notes and you'll observe several different types with disparate goals:
Shorthand: A memory mechanism to simplify/summarize a complex text.
Logbook: Record a series of events which occurred and what order.
Planner: Todo lists, upcoming meetings, due dates.
Whiteboard: A worksheet for working through a complex problem.
Time-capsule: Long term memory about why we decided to do [thing].
If you take someone who treats notes like a Whiteboard and try to sell them a system which looks like a Logbook, they will think it makes no sense.
This website is somewhere between long-term memory and shorthand, a collection of things I will want to reference later.