I see several advantages :
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Tool discoverability: having tools displayed in the left toolbar helps make (new) Blender users clearly know about that the tool exists.
Working with hotkeys is just one way to use Blender, the other way is by using menus and toolbars.
The user shouldn’t have to discover this feature (nor the hotkey) only by reading the documentation or by randomly noticing it in a menu.
IMO, having an “eyedropper color picker” in the toolbar makes sense for Blender users who prefer using GUIs. -
for Blender users who use a digital pen