Oh, sure, I don’t mean “why does this app exist”; I mean “why isn’t its underlying data model merged/synchronized with that of the other OS note-taking app.” Why can’t I see my computer’s Sticky Notes on my iPhone in Notes under “Sticky Notes - [Computer name]”? Why can’t I add a sticky note to my computer by putting it in such a folder?
It might be that the future of sticky notes is Quick Notes as in iOS 15, but they do different things, I agree. Apple really should integrate the concept of sticky notes into both Notes and Reminders, to create a bit of a hybrid - a sticky note that can act as a reminder, etc. Even better would be sticky notes that reveal themselves when using certain macOS or iOS modes, so that when I’m at work I see my work stickies, and when I’m at home I could see some home stickies, etc. It should also be easy to remove a sticky by converting it permanently to a note or reminder, or maybe even a calendar event or contact.