RobotFramework: Why write tests in keywords/robot-framework synteax at all?

I'm not asking why we should use RobotFramework at all, I'm only asking why we should write tests using their syntax and not write tests entirely as custom libraries.

Say we want to write a test that looks at a directory and ensures that no files in that directory have been changed. You can write it in RobotFramework with their Get Files In Directory and Get Modified Time keywords and its syntax for writing loops, or you could just write your own test that does that entirely in Python (loops through files in a directory and ensures that each file's modified time is before when you run any code you're testing).

As a Python developer (and not RobotFramework developer), I want to default to writing everything in Python and use the RobotFramework syntax only to check if those custom tests are True, False, etc. (Just out of comfort.)