Why MERN better than React+Flask or React+Django?

I am a student and excited about ML stuff. But most of the time when I reach out to my fellow mates for any project they just tell me that they prefer MERN over React+Flask or React+Django. I haven't got any satisfying answer to this thing though that ,why they prefer MERN, as for me if I want to integrate my ML model with my website I would prefer React+Django/Flask for it.