It can also be due to tooling -- once a student has got the python binary installed you can get them writing and running code without having to make sure they have the correct version of x, y, z (don't even need conda or pip) or teaching them what a compiler is etc.
Javascript is quite popular as an introductory language too -- students can open up a web browser and type stuff in the console in the middle of a lecture.
I agree. It even features a basic IDE, IDLE, as part of the default install. No need to figure out how to configure your text editor to interact with the Python shell. I remember trying to learn Ruby before Python, several years ago, but then got stuck trying to configure Geany to work with Ruby.
Javascript is quite popular as an introductory language too -- students can open up a web browser and type stuff in the console in the middle of a lecture.