Because I dislike interspersing executable statements at module level with function definitions. I’d rather have all code live inside functions and have one main entry point for the script. It’s just a personal preference, nothing wrong with not doing that though.

But you could have a single main() call without the if statement, couldn't you?

REPL-based development. You might be developing a script, but notice a bug. If you import your script as a module, you can run the function you’re debugging, figure out what’s wrong, edit the file, and then reimport the module (using importlib.reload).

Okay, that's quite convincing, thanks!