At the same time, it makes some sense... the programmers for a system aren't always the best users of a system. So if you're expecting them to dogfood their own system (Google Sheets), you might find that they test/interact with the system primarily through the API and not the GUI.

I have no idea if they do or not, but it's a plausible explanation...

Use case feels like the wrong term.

Do you mean restricted workflow? Googles APIs are pretty much 1:1 to the GUI

And using Python makes it trivial to copy-paste out of files and other APIs with one run of Python

Versus all the fiddling in browser tabs with a mouse, it actually affords an incredibly wide set of options to quickly collate and format data