Practically all of the most popular and widely used deep-learning frameworks are implemented in Python on the surface and C/C++ under the hood.
I think the main reason is that Python is widely used in scientific and research communities and it may be easier, because it's easy to experiment with new ideas and code prototypes quickly in a language with minimal syntax like Python.
Moreover there may be another reason. As I can see, most of the over-hyped online courses on AI are pushing Python because it is easy for newbie programmers. AI is the new marketing hot word to sell programming courses. ( Mentioning AI can sell programming courses for peopleto kids who want to build HAL 3000, but can not even write even a Hello World! or drop a trend-line onto an Excel graph. :)