[Rust]

I'm no Python expert, but the only reason I can think of is a combination of developer inertia and tradition.

In most IDEs, a TAB can be displayed as any number of equivalent spaces (8 being the common indent size), so if I switch back and forth between my big monitor (8) and my laptop screen (4), I can view the code with an indent relative to the width of the screen.

If that code uses spaces, I'm usually stuck seeing an indent of 4 on the big screen monitor - something I find irritating because it makes it harder to visually scan and parse code quickly.

So, even in Python, I always use TABs whenever I have the choice. It's just more flexible.