I never understood the hiring practices of most software/technology companies. Why does a guy that actively contributes to open source software in multiple lang

I never understood the hiring practices of most software/technology companies. Why does a guy that actively contributes to open source software in multiple languages have to take a technical interview? Do people hiring at these companies not look at GitHub? Feels like it would be better to hire people based on their code and contributions on GitHub over how well they perform on a technical interview. Someone submitting bug fixes to libraries is probably one of the best type of programmer you can hire. I'm lucky I never had to do this shit to get a job lol.