Over the years Python has taken most of the science community thanks to godly libraries (NumPy, SciPy, etc). Also, Python has one of the simpliest syntax of programming languages. It's interpreted so it does not need compiling. Also multiparadigms so you can code as you like (OOP, Funtional, Imperative)
Machine Learning is being researched mostly by computer scientist. I think when most of them start researching they look up for the easiest language, so they dont waste time learning the language and they can go straight to do their work.