I'll turn it around and ask why, for simple tasks, is the CLI any better than a GUI ignoring personal preferences?
For me, the main thing is speed: I can type much faster than I can navigate a cursor (tab completion helps). I recognise that some GUIs have keyboard shortcuts to speed things up, but then at some point you're using the keyboard enough to justify using a CLI. The other thing is that I don't find graphical representations of my changes helpful at all. I commit early, commit often, so the output of `git diff` generally doesn't need to be paginated. My feature branches are small so I can merge them without the need to see a commit/branch graph.
To be honest it's hard to answer that without ignoring personal preferences because really, that's all it boils down to.
I can definitely understand the want to use a GUI when you're doing complex adds or merges. spacemanaki is right in saying that doing this a lot probably indicates a problem with workflow, though.