Why do so many namespaces start with com

Question

I've noticed that a lot of companies use "reverse domain name" namespaces and I'm curious where that practice originated and why it continues. Does it merely continue because of rote practice, or is there an outstanding architecture concept I might be missing here?

Also note questions such as: https://stackoverflow.com/questions/189209/do-you-really-use-your-reverse-domain-for-package-naming-in-java that sort of answer my question but not 100%

_{(If it makes you feel any better, I'm really curious if I should be using it for my javascript namespacing efforts, but I'm more curious about then when and why, and that should help guide me on the javascript answer, nota bene: "window")}

Example of this practice extending to folders and files: