How to remove extra brushes from the Brush Tip Shape sub-tab of the Brush tab and leave only one of the Brush Presets?

Question

Adobe

Brush Presets contains only one brush, but the Brush Tip Shape sub-tab of the Brush tab contains 21 brushes for some reason.
Here in this dialog I pressed ok.

And I still can’t remove the sets I don’t need from the Brush Tip Shape sub-tab of the Brush tab, what should I do? I want to leave one brush here and there, but these 20 extra brushes are really stressing me out, especially in my set. I also noticed that they fit into any set of brushes. What are these brushes, why are they so ubiquitous, and can they be removed, if so, how?